Variable Interest Entities (Aggregate Assets, Liabilities and Maximum Exposure to Loss) (Details) - USD ($) $ in Millions	Mar. 31, 2020	Dec. 31, 2019
Variable Interest Entity [Line Items]
Total assets	$ 370,779	$ 294,005
Liabilities	344,509	272,260
Variable Interest Entity, Not Primary Beneficiary [Member]
Variable Interest Entity [Line Items]
Total assets	630	636
Liabilities	261	275
Maximum exposure to loss	665	670
Variable Interest Entity, Not Primary Beneficiary [Member] | LIHTC Investments [Member]
Variable Interest Entity [Line Items]
Total assets	513	516
Liabilities	261	275
Maximum exposure to loss	513	516
Variable Interest Entity, Not Primary Beneficiary [Member] | Other CRA Investments [Member]
Variable Interest Entity [Line Items]
Total assets	117	120
Liabilities	0	0
Maximum exposure to loss	$ 152	$ 154