Commitment and Contingencies - Narrative - (Details) - USD ($) $ in Millions	Mar. 31, 2020	Dec. 31, 2019
Other Commitments [Line Items]
Assets	$ 506,229	$ 473,078
Other Liabilities	11,631	12,236
Trading Assets	3,863	5,733
Variable Interest Entity, Primary Beneficiary [Member]
Other Commitments [Line Items]
Assets	2,100	2,700
Other Liabilities	153	116
Trading Assets	1,400	$ 2,600
Buildings and building improvements
Loss Contingency [Abstract]
Buildings and Improvements, Gross	456
Min
Loss Contingency [Abstract]
Loss Contingency, Range of Possible Loss, Portion Not Accrued	0
Max
Loss Contingency [Abstract]
Loss Contingency, Range of Possible Loss, Portion Not Accrued	$ 200