Income Taxes (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2019	Mar. 31, 2018	Dec. 31, 2018
Operating Loss Carryforwards [Line Items]
Effective tax rate on income from continuing operations (as a percent)	15.90%	14.70%
Valuation allowance	$ 20		$ 20
Gross unrecognized tax benefits	92		92
Unrecognized tax benefits net of federal tax benefits that would affect the effective tax rate	71		70
Increase (decrease) in interest and penalties	1	$ 1
Payable related to accrued interest and penalties	11		$ 10
Minimum [Member]
Operating Loss Carryforwards [Line Items]
Decrease in gross unrecognized tax benefits due to resolution of audits and statute expirations	30
Maximum [Member]
Operating Loss Carryforwards [Line Items]
Decrease in gross unrecognized tax benefits due to resolution of audits and statute expirations	40
State and Local [Member]
Operating Loss Carryforwards [Line Items]
State net operating losses	$ 21