Quarterly report pursuant to Section 13 or 15(d)

Debt and Secured Revolving Line of Credit (Narrative) (Details)

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Debt and Secured Revolving Line of Credit (Narrative) (Details)
1 Months Ended 3 Months Ended 9 Months Ended
Apr. 14, 2015
USD ($)
Sep. 30, 2016
USD ($)
day
Sep. 29, 2018
USD ($)
$ / shares
Sep. 29, 2018
USD ($)
$ / shares
Sep. 30, 2017
USD ($)
Jun. 29, 2018
$ / shares
Dec. 30, 2017
USD ($)
Jun. 16, 2014
USD ($)
Feb. 26, 2014
USD ($)
Aug. 15, 2012
USD ($)
Debt Instrument [Line Items]                    
Issuance of treasury stock to partially settle debt [1],[2]       $ 103,000,000 $ 38,000,000          
Gain (Loss) on extinguishment of debt     $ 6,000,000 7,000,000            
Aggregate principal amount repurchased [1],[2]       15,000,000 $ 70,000,000          
Secured Revolving Line of Credit                    
Debt Instrument [Line Items]                    
Secured revolving line of credit, outstanding balance     $ 70,000,000 $ 70,000,000     $ 70,000,000      
Secured revolving line of credit, interest rate     5.50% 5.50%     4.75%      
Letters of credit outstanding, amount     $ 26,000,000 $ 26,000,000            
Secured revolving line of credit, remaining borrowing capacity     205,000,000 $ 205,000,000            
Repayment period       90 days            
Secured Revolving Line of Credit | Amended and restated loan and security agreement                    
Debt Instrument [Line Items]                    
Maximum borrowing capacity $ 500,000,000                  
Maximum letters of credit available for issuance 45,000,000                  
Aggregate amount by which size of commitments may be increased (up to) $ 200,000,000                  
Secured Revolving Line of Credit | Amended and restated loan and security agreement | Federal Funds Rate                    
Debt Instrument [Line Items]                    
Basis spread on variable rate 0.50%                  
Secured Revolving Line of Credit | Amended and restated loan and security agreement | LIBOR                    
Debt Instrument [Line Items]                    
Basis spread on variable rate 1.00%                  
2.125% Convertible Senior Notes due 2026                    
Debt Instrument [Line Items]                    
Stated interest rate   2.125%                
Principal amount   $ 805,000,000 $ 805,000,000 $ 805,000,000     $ 805,000,000      
Outstanding aggregate principal amount   $ 805,000,000                
Debt Instrument, Convertible, Conversion Price | $ / shares     $ 8.00 $ 8.00            
Remaining life       96 months            
Share price (in usd per share) | $ / shares           $ 30.89        
If-converted value in excess of principal     $ 2,303,000,000              
Effective interest rate     8.00% 8.00%            
2.125% Convertible Senior Notes due 2026 | Debt Instrument, circumstance 1                    
Debt Instrument [Line Items]                    
Threshold trading days | day   20                
Threshold consecutive trading days | day   30                
Threshold percentage of conversion price   130.00%                
2.125% Convertible Senior Notes due 2026 | Debt Instrument, circumstance 2                    
Debt Instrument [Line Items]                    
Threshold consecutive trading days | day   10                
Threshold percentage of conversion price   98.00%                
Conversion period after threshold period days | day   5                
6.75% Senior Notes due 2019                    
Debt Instrument [Line Items]                    
Stated interest rate                 6.75%  
Repayments of Debt       $ 14,000,000            
Issuance of treasury stock to partially settle debt     $ 87,000,000              
Principal amount                 $ 600,000,000  
Outstanding aggregate principal amount     66,000,000 66,000,000            
Aggregate principal amount settled       101,000,000            
7.50% Senior Notes due 2022                    
Debt Instrument [Line Items]                    
Stated interest rate                   7.50%
Principal amount                   $ 500,000,000
Outstanding aggregate principal amount     337,000,000 337,000,000            
Aggregate principal amount settled     10,000,000              
7.00% Senior Notes due 2024                    
Debt Instrument [Line Items]                    
Stated interest rate               7.00%    
Principal amount               $ 500,000,000    
Outstanding aggregate principal amount     310,000,000 $ 310,000,000            
Aggregate principal amount repurchased     $ 1,000,000              
[1] Amounts reflected adoption of ASU 2016-18, Statement of Cash Flows, Restricted Cash (Topic 230) beginning in the first quarter of 2018.
[2] Prior year amounts adjusted to reflect the retrospective application of ASU 2014-09, Revenue from Contracts with Customers. Refer to Note 1.