Stock-based Compensation Expense (Details) (USD $) In Millions, except Share data, unless otherwise specified	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011
Share-based Compensation Arrangement by Share-based Payment Award, Options, Grants in Period, Net of Forfeitures [Abstract]
Share-based Compensation Arrangement by Share-based Payment Award, Number of Shares Authorized			4,687,500
Share-based Compensation Arrangement by Share-based Payment Award, Number of Shares Available for Grant			3,701,833
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Vested in Period, Total Fair Value			$ 4	$ 3	$ 1
Share-based Compensation	1	3	4	4	4
Adjustments Related to Tax Withholding for Share-based Compensation			2	1	1
Employee Service Share-based Compensation, Nonvested Awards, Total Compensation Cost Not yet Recognized			4
Stock-based Compensation, Attainment of Performance Goals That Allows Vesting			110.70%	109.20%	107.80%
Stock-based Compensation, Forfeiture Rate			5.00%
Share-based Compensation Arrangement by Share-based Payment Award, Options, Grants in Period, Weighted Average Grant Date Fair Value			99.70%
Employee Service Share-based Compensation, Allocation of Recognized Period Costs, Capitalized Amount			0	0	0
stock based compensation impact on cash flows			$ 0	$ 0	$ 0
Performance based stock award percentage - minimum			0.00%
Performance based stock award percentage - maximum			150.00%