Income Taxes (Narrative) (Details) $ in Millions	3 Months Ended
	Mar. 31, 2018 USD ($)	Dec. 31, 2017 USD ($)
Income Tax Disclosure [Abstract]
Income tax rate	23.20%
Decrease in income tax percentage	0.098
Tax Cuts and Jobs Act, net tax benefits	$ 11
Unrecognized tax benefits	68	$ 66
Unrecognized tax benefits that would impact the effective tax rate	45	43
Unrecognized tax benefits that would impact deferred taxes	23	$ 23
Possible decrease in unrecognized tax benefits	$ 16