Income Taxes (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2019	Jun. 30, 2018	Jun. 30, 2019	Jun. 30, 2018	Dec. 31, 2018
Operating Loss Carryforwards [Line Items]
Effective tax rate on income from continuing operations (as a percent)	16.10%	15.70%	16.00%	15.20%
Valuation allowance	$ 21		$ 21		$ 20
Gross unrecognized tax benefits	117		117		92
Unrecognized tax benefits net of federal tax benefits that would affect the effective tax rate	81		81		70
Increase (decrease) in interest and penalties	1	$ 0	2	$ 1
Payable related to accrued interest and penalties	12		12		$ 10
Minimum [Member]
Operating Loss Carryforwards [Line Items]
Decrease in gross unrecognized tax benefits due to resolution of audits and statute expirations	50		50
Maximum [Member]
Operating Loss Carryforwards [Line Items]
Decrease in gross unrecognized tax benefits due to resolution of audits and statute expirations	60		60
State and Local [Member]
Operating Loss Carryforwards [Line Items]
State net operating losses	$ 21		$ 21