Income Taxes - Affordable Housing Tax Credits (Details) - USD ($) $ in Billions	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Income Tax Disclosure [Abstract]
Tax credit and other tax benefits	$ 1.5	$ 1.5	$ 1.5
Amount of amortization reported in income tax expense	1.2	1.1	$ 1.2
Carrying value of investments, reported in other assets	9.7	8.6
Amount of commitments, reported in account payable and other liabilities	$ 3.8	$ 2.8