Share-Based Compensation (RSU Activity) (Details) - RSUs - USD ($) $ / shares in Units, shares in Thousands, $ in Millions	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Period of straight-line expense, 2015 RSU's	3 years
Employee Service Share-based Compensation, Nonvested Awards, Compensation Cost Not yet Recognized, Period for Recognition	1 year 9 months 18 days
RSUs (Number of Shares):
Nonvested at beginning of period	2,392
Vested	(1,063)	(954)	(1,037)
Forfeited and expired	(256)
Granted	1,964
Nonvested at end of period	3,037	2,392
Vested and expected to vest at end of period	2,716
Employee Service Share-based Compensation, Nonvested Awards, Compensation Cost Not yet Recognized	$ 17
Weighted Average Grant Date Fair Value (in dollars per share):
Nonvested at beginning of period	$ 12.55
Vested	12.43
Forfeited and expired	10.91
Granted	9.42	$ 12.03	$ 14.60
Nonvested at end of period	10.70	$ 12.55
Vested and expected to vest at end of period	$ 10.76
Nonvested at end of period, weighted average remaining vesting term	20 months