Income Taxes Income Taxes (Narrative) (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017	Dec. 31, 2017
Income Tax Disclosure [Abstract]
Effective Income Tax Rate Reconciliation, Percent	18.01%	32.24%	21.37%	31.19%
Effective Income Tax Rate Reconciliation, at Federal Statutory Income Tax Rate, Percent	21.00%	35.00%	21.00%	35.00%
Amortization Method Qualified Affordable Housing Project Investments	$ 59		$ 59		$ 64
Qualified Affordable Housing Project Investments, Commitment	17		17		$ 26
Variable Interest Entity, Reporting Entity Involvement, Maximum Loss Exposure, Amount	$ 72		$ 72