Share-Based Compensation (RSU Compensation Expense) (Details) - RSUs - USD ($) $ in Millions		12 Months Ended
		Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Pretax compensation expense		$ 13	$ 12	$ 12
Tax benefit		(3)	(3)	(3)
Total expense, net of tax		10	9	9
Total value of RSUs converted	[1]	16	25	10
Total fair value of RSUs vested		$ 12	$ 13	$ 12

[1] (1)Amount represents fair market value on the date of conversion.