Income Taxes (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2017	Jun. 30, 2016	Jun. 30, 2017	Jun. 30, 2016	Dec. 31, 2016
Operating Loss Carryforwards [Line Items]
Effective tax rate on income from continuing operations (as a percent)	23.10%	18.40%	19.30%	21.00%
Benefit from completion of audits		$ 17
Adoption impact of stock compensation accounting guidance	$ (118)	(75)	$ (190)	$ (186)
Valuation allowance	12		12		$ 11
Gross unrecognized tax benefits	119		119		115
Unrecognized tax benefits net of federal tax benefits that would affect the effective tax rate	49		49		46
Increase (decrease) in interest and penalties	0	$ 0	1	(44)
Payable related to accrued interest and penalties	9		9		$ 8
Minimum [Member]
Operating Loss Carryforwards [Line Items]
Decrease in gross unrecognized tax benefits due to resolution of audits and statute expirations	20		20
Maximum [Member]
Operating Loss Carryforwards [Line Items]
Decrease in gross unrecognized tax benefits due to resolution of audits and statute expirations	30		30
State and Local [Member]
Operating Loss Carryforwards [Line Items]
State net operating losses	15		15
Adjustments for new accounting pronouncement [Member]
Operating Loss Carryforwards [Line Items]
Adoption impact of stock compensation accounting guidance	$ 4		$ 32	$ 5