Equity (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Increase (decrease) in common stock, number of shares
Balance at the beginning of the period	77,810,875
Purchase/acquisition of treasury stock	(1,000,000)	0
Balance at the end of the period	77,810,875	77,810,875
Share-based compensation expense
Pre-tax compensation expense	$ 26	$ 28	$ 21
Income tax benefit	(8)	(11)	(8)
Total share-based compensation expense, net of income taxes	$ 18	$ 17	$ 13
Stock Incentive Plan
Shares Authorized Under Stock Incentive Plan	8,000,000
Shares available for future grants under Stock Incentive Plan	3,700,000
Common Stock Issued
Increase (decrease) in common stock, number of shares
Balance at the beginning of the period	77,811,000	77,811,000	77,811,000
Balance at the end of the period	77,811,000	77,811,000	77,811,000
Treasury Stock
Increase (decrease) in common stock, number of shares
Balance at the beginning of the period	5,397,000	6,195,000	6,489,000
Issuance of restricted stock units as compensation	(103,000)	(94,000)	(102,000)
Performance shares and other share-based awards	(75,000)	(70,000)	(75,000)
Stock options exercised	(443,000)	(636,000)	(556,000)
Purchase/acquisition of treasury stock	1,039,000	2,000	439,000
Balance at the end of the period	5,815,000	5,397,000	6,195,000
Common Stock Shares Outstanding
Increase (decrease) in common stock, number of shares
Balance at the beginning of the period	72,414,000	71,616,000	71,322,000
Issuance of restricted stock units as compensation	103,000	94,000	102,000
Performance shares and other share-based awards	75,000	70,000	75,000
Stock options exercised	443,000	636,000	556,000
Purchase/acquisition of treasury stock	(1,039,000)	(2,000)	(439,000)
Balance at the end of the period	71,996,000	72,414,000	71,616,000
Employee Stock Option
Increase (decrease) in common stock, number of shares
Stock options exercised	443,000
Share-based compensation expense
Pre-tax compensation expense	$ 7	$ 9	$ 7
Income tax benefit	(2)	(3)	(3)
Total share-based compensation expense, net of income taxes	5	6	4
Restricted Stock Units (RSUs)
Share-based compensation expense
Pre-tax compensation expense	13	12	9
Income tax benefit	(4)	(5)	(3)
Total share-based compensation expense, net of income taxes	9	7	6
Performance shares and other share-based awards
Share-based compensation expense
Pre-tax compensation expense	6	7	5
Income tax benefit	(2)	(3)	(2)
Total share-based compensation expense, net of income taxes	$ 4	$ 4	$ 3