Variable Interest Entities (Aggregate Assets, Liabilities and Maximum Exposure to Loss) (Details) - USD ($) $ in Millions		Dec. 31, 2020	Dec. 31, 2019
Variable Interest Entity [Line Items]
Assets	[1]	$ 549,009	$ 294,005
Liabilities	[1]	492,949	272,260
Variable Interest Entity, Not Primary Beneficiary [Member]
Variable Interest Entity [Line Items]
Assets		767	636
Liabilities		344	275
Maximum exposure to loss		801	670
LIHTC Investments [Member] | Variable Interest Entity, Not Primary Beneficiary [Member]
Variable Interest Entity [Line Items]
Assets		649	516
Liabilities		344	275
Maximum exposure to loss		649	516
Other CRA Investments [Member] | Variable Interest Entity, Not Primary Beneficiary [Member]
Variable Interest Entity [Line Items]
Assets		118	120
Liabilities		0	0
Maximum exposure to loss		$ 152	$ 154

[1] Certain prior year amounts have been reclassified to conform to the current year presentation. See Note 1 for additional information.