Equity - Additional Information (Details) - USD ($) $ / shares in Units, $ in Millions	3 Months Ended								12 Months Ended
	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Schedule of Earnings Per Share, Basic and Diluted, by Common Class [Line Items]
Share Based Compensation Arrangement By Share Based Payment Award Equity Instruments Other Than Options Repurchased In Period									235,066
Common Stock Repurchased - Amount									$ 0	$ 18	$ 32
Common Stock Repurchased - Shares Repurchased									0	1,200,000	2,000,000
Common Stock Repurchased - Weighted Average Cost Per Share									$ 0.00	$ 15.29	$ 15
Dividends, Common Stock									$ 132	$ 132	$ 133
Common Stock, Dividends, Per Share, Declared	$ 0.25	$ 0.25	$ 0.25	$ 0.25	$ 0.25	$ 0.25	$ 0.25	$ 0.25	$ 1.00	$ 1.00	$ 1.00
Common Stock, Shares, Issued	136,000,000				136,000,000				136,000,000	136,000,000
Common stock, shares outstanding	131,000,000				130,000,000				131,000,000	130,000,000
Common Stock, Capital Shares Reserved for Future Issuance	4,000,000								4,000,000
Preferred stock, shares authorized	10,000,000				10,000,000				10,000,000	10,000,000
Restricted Stock [Member]
Schedule of Earnings Per Share, Basic and Diluted, by Common Class [Line Items]
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Grants in Period									813,816
Restricted Stock Units (RSUs) [Member]
Schedule of Earnings Per Share, Basic and Diluted, by Common Class [Line Items]
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Grants in Period									624,000