Income Taxes - Affordable Housing Tax Credits (Details) - USD ($) $ in Billions	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Income Tax Disclosure [Abstract]
Tax credit and other tax benefits	$ 1.5	$ 1.5	$ 1.7
Amount of amortization reported in income tax expense	1.1	1.2	$ 1.7
Carrying value of investments, reported in other assets	8.6	7.9
Amount of commitments, reported in account payable and other liabilities	$ 2.8	$ 2.3