Debt - Repurchase of Senior Notes and Issuance of Senior Notes (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2016		Dec. 31, 2015	Dec. 31, 2014	Mar. 31, 2015	Feb. 24, 2015
Debt Instrument [Line Items]
Loss on early extinguishment of debt	$ 37		$ 19	$ 0
Debt issuance cost	6		13
Long term debt net of unamortized debt issuance costs	$ 1,083		$ 2,175
6.3% senior notes due 2016
Debt Instrument [Line Items]
Stated interest rate	6.30%		6.30%
Repurchase amount	$ 500
Premiums paid on early redemption of debt	30
Accrued interest on early redemption of debt	$ 9
7.875% senior notes due 2020
Debt Instrument [Line Items]
Stated interest rate	7.875%		7.875%
Repurchase amount	$ 250
5.875% senior notes due 2021
Debt Instrument [Line Items]
Stated interest rate	5.875%		5.875%
Repurchase amount	$ 350
8.375% senior notes due 2018
Debt Instrument [Line Items]
Stated interest rate	8.375%
Repurchase amount					$ 350
Aggregate consideration						$ 377
5.5% senior notes due 2025
Debt Instrument [Line Items]
Stated interest rate	5.50%	[1]	5.50%
Face amount of notes						350
Debt issuance cost						$ 6
Long term debt net of unamortized debt issuance costs	$ 345		$ 344

[1] Callable at any time prior to the call date at a price equal to 100% of the principal plus a premium (as outlined in the respective indentures), plus any accrued and unpaid interest on the principal amount being called. Callable after the call date at stated redemption prices (as outlined in the applicable indenture), plus any accrued and unpaid interest on the principal amount being called.