Equity (Narrative) (Details) - USD ($)	12 Months Ended
	Dec. 31, 2017	Nov. 30, 2017
Equity Class Of Treasury Stock [Line Items]
Purchase of common stock value under the share repurchase program	$ 116,000,000
Cash dividend declared, per share	$ 0.17
Accrued dividend payable	$ 31,000,000
Common Stock [Member]
Equity Class Of Treasury Stock [Line Items]
Stock repurchase program effective date	Nov. 30, 2017
Stock repurchase program expiration date	Dec. 31, 2020
Purchase of common stock under the share repurchase program	2,386,406
Purchase of common stock value under the share repurchase program	$ 116,000,000
Average share price	$ 48.81
Purchase of common stock under the share repurchase program, share Settled	206,106
Purchase of common stock value under the share repurchase program, for share Settled	$ 10,000,000
Remaining available amount of common stock under the share repurchase program	384,000,000
Cash dividend declared, per share		$ 0.17
Accrued dividend payable	$ 31,000,000
Common Stock [Member] | Maximum [Member]
Equity Class Of Treasury Stock [Line Items]
Stock repurchase program, authorized amount		$ 500,000,000