Variable Interest Entities (Aggregate Assets, Liabilities and Maximum Exposure to Loss) (Details) - USD ($) $ in Millions	Sep. 30, 2020	Dec. 31, 2019
Variable Interest Entity [Line Items]
Total assets	$ 419,355	$ 294,005
Liabilities	388,024	272,260
Variable Interest Entity, Not Primary Beneficiary [Member]
Variable Interest Entity [Line Items]
Total assets	699	636
Liabilities	292	275
Maximum exposure to loss	734	670
Variable Interest Entity, Not Primary Beneficiary [Member] | LIHTC Investments [Member]
Variable Interest Entity [Line Items]
Total assets	583	516
Liabilities	292	275
Maximum exposure to loss	583	516
Variable Interest Entity, Not Primary Beneficiary [Member] | Other CRA Investments [Member]
Variable Interest Entity [Line Items]
Total assets	116	120
Liabilities	0	0
Maximum exposure to loss	$ 151	$ 154