Share-Based Compensation Expense (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017
Share-based compensation expense
Pre-tax compensation expense	$ 5	$ 7
Income tax benefit	(1)	(3)
Total share-based compensation expense, net of income taxes	4	4
Employee Stock Option
Share-based compensation expense
Pre-tax compensation expense	1	2
Income tax benefit		(1)
Total share-based compensation expense, net of income taxes	1	1
Restricted Stock Units (RSUs)
Share-based compensation expense
Pre-tax compensation expense	3	3
Income tax benefit	(1)	(1)
Total share-based compensation expense, net of income taxes	2	2
Performance shares and other share-based awards
Share-based compensation expense
Pre-tax compensation expense	1	2
Income tax benefit		(1)
Total share-based compensation expense, net of income taxes	$ 1	$ 1