Variable Interest Entities (Aggregate Assets, Liabilities and Maximum Exposure to Loss) (Details) - USD ($) $ in Millions	Jun. 30, 2020	Dec. 31, 2019
Variable Interest Entity [Line Items]
Total assets	$ 400,484	$ 294,005
Liabilities	369,669	272,260
Variable Interest Entity, Not Primary Beneficiary [Member]
Variable Interest Entity [Line Items]
Total assets	649	636
Liabilities	269	275
Maximum exposure to loss	685	670
Variable Interest Entity, Not Primary Beneficiary [Member] | LIHTC Investments [Member]
Variable Interest Entity [Line Items]
Total assets	533	516
Liabilities	269	275
Maximum exposure to loss	533	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	$ 152	$ 154