Income Taxes (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2016	Jun. 30, 2015	Jun. 30, 2016	Jun. 30, 2015	Dec. 31, 2015
Operating Loss Carryforwards [Line Items]
Effective tax rate on income from continuing operations (as a percent)	18.40%	22.60%	21.00%	22.60%
Benefits Tax Planning and Completion of Audits	$ 17		$ 17
Valuation allowance	11		11		$ 11
Gross unrecognized tax benefit (expense)	119		119		161
Unrecognized tax benefits (net of federal tax benefits) that would impact the effective tax rate	50		50		57
Increase (reduction) in interest and penalties	0	$ 1	44	$ 2
Accrued interest and penalties	7		7		$ 51
Minimum [Member]
Operating Loss Carryforwards [Line Items]
Decrease in gross unrecognized tax benefits due to resolution of IRS examination	60		60
Maximum [Member]
Operating Loss Carryforwards [Line Items]
Decrease in gross unrecognized tax benefits due to resolution of IRS examination	70		70
State and Local [Member]
Operating Loss Carryforwards [Line Items]
State net operating losses	$ 15		$ 15