Share-Based Compensation Narrative (Details) - USD ($) $ / shares in Units, shares in Thousands, $ in Millions	1 Months Ended	12 Months Ended
	Jun. 30, 2016	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Number of shares available for grant under Incentive Plans		33,000
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Nonvested, Weighted Average Grant Date Fair Value		$ 0	$ 0	$ 0
Employee Stock [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Number of shares authorized (in shares)	12,000
Offering period	6 months
Purchase price percent	90.00%
Stock Issued During Period, Shares, Share-based Compensation, Gross		3,000
Maximum [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Maximum term (in years) that awards will be granted		10 years
Employee Stock Option [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Intrinsic value of stock options exercised				$ 15
Share-based Compensation Arrangement by Share-based Payment Award, Options, Exercises in Period		0	0
Employee Stock Option [Member] | Minimum [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Award vesting period		1 year
Employee Stock Option [Member] | Maximum [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Award vesting period		4 years
Restricted Stock and Restricted Stock Units (RSUs) [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Weighted-average grant date fair value			$ 4.26	$ 6.2	$ 11.94
Total fair value of awards vested during the period			$ 30	$ 38	$ 37
Unrecognized compensation expense			$ 59
Unrecognized compensation expense, recognition period			2 years
Restricted Stock and Restricted Stock Units (RSUs) [Member] | Minimum [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Award vesting period			3 years
Performance units [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Award vesting period		3 years
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Nonvested, Weighted Average Grant Date Fair Value		$ 6.07	$ 7.08
Award vesting		200.00%
Weighted-average grant date fair value		$ 6.06	$ 5.11	$ 10.45
Unrecognized compensation expense		$ 9
Unrecognized compensation expense, recognition period		1 year
Risk-free interest rate		1.17%
Volatility rate		67.00%
Dividend yield		0.00%
Shares issued for share-based compensation awards (in shares)		145