Income Taxes (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2016	Mar. 31, 2015	Dec. 31, 2015
Operating Loss Carryforwards [Line Items]
Effective tax rate on income from continuing operations (as a percent)	23.30%	22.50%
Valuation allowance	$ 11		$ 11
Gross unrecognized tax benefit (expense)	124		161
Unrecognized tax benefits (net of federal tax benefits) that would impact the effective tax rate	57		57
Increase (reduction) in interest and penalties	(44)	$ 1
Accrued interest and penalties	7		$ 51
Minimum [Member]
Operating Loss Carryforwards [Line Items]
Decrease in gross unrecognized tax benefits due to resolution of IRS examination	50
Maximum [Member]
Operating Loss Carryforwards [Line Items]
Decrease in gross unrecognized tax benefits due to resolution of IRS examination	60
State and Local [Member]
Operating Loss Carryforwards [Line Items]
State net operating losses	$ 16