Income Taxes (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2017	Sep. 30, 2016	Dec. 31, 2016
Operating Loss Carryforwards [Line Items]
Effective tax rate on income from continuing operations (as a percent)	19.90%	9.70%	19.50%	18.60%
Adoption impact of stock compensation accounting guidance	$ (125)	$ (23)	$ (315)	$ (209)
Valuation allowance	14		14		$ 11
Gross unrecognized tax benefits	127		127		115
Unrecognized tax benefits net of federal tax benefits that would affect the effective tax rate	55		55		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	15		15
Maximum [Member]
Operating Loss Carryforwards [Line Items]
Decrease in gross unrecognized tax benefits due to resolution of audits and statute expirations	25		25
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	$ 25		$ 57	$ 8