Variable Interest Entities (Aggregate Assets, Liabilities and Maximum Exposure to Loss) (Details) - USD ($) $ in Millions	Sep. 30, 2021	Dec. 31, 2020
Variable Interest Entity [Line Items]
Aggregate assets	$ 607,548	$ 549,009
Aggregate liabilities	550,106	492,949
Variable Interest Entity, Not Primary Beneficiary [Member]
Variable Interest Entity [Line Items]
Aggregate assets	972	767
Aggregate liabilities	495	344
Maximum exposure to loss	999	801
Variable Interest Entity, Not Primary Beneficiary [Member] | LIHTC Investments [Member]
Variable Interest Entity [Line Items]
Aggregate assets	839	649
Aggregate liabilities	495	344
Maximum exposure to loss	839	649
Variable Interest Entity, Not Primary Beneficiary [Member] | Other CRA Investments [Member]
Variable Interest Entity [Line Items]
Aggregate assets	133	118
Aggregate liabilities	0	0
Maximum exposure to loss	$ 160	$ 152