Variable Interest Entities (Aggregate Assets, Liabilities and Maximum Exposure to Loss) (Details) - USD ($) $ in Millions	Jun. 30, 2021	Dec. 31, 2020
Variable Interest Entity [Line Items]
Aggregate assets	$ 574,532	$ 549,009
Aggregate liabilities	517,082	492,949
Variable Interest Entity, Not Primary Beneficiary [Member]
Variable Interest Entity [Line Items]
Aggregate assets	921	767
Aggregate liabilities	461	344
Maximum exposure to loss	939	801
Variable Interest Entity, Not Primary Beneficiary [Member] | LIHTC Investments [Member]
Variable Interest Entity [Line Items]
Aggregate assets	785	649
Aggregate liabilities	461	344
Maximum exposure to loss	785	649
Variable Interest Entity, Not Primary Beneficiary [Member] | Other CRA Investments [Member]
Variable Interest Entity [Line Items]
Aggregate assets	136	118
Aggregate liabilities	0	0
Maximum exposure to loss	$ 154	$ 152