Variable Interest Entities (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2021	Mar. 31, 2020	Dec. 31, 2020
Variable Interest Entity [Line Items]
Variable interest entity, other short-term borrowings	$ 610		$ 620
Weighted average life of trusts	2 years 4 months 24 days	2 years 8 months 12 days
Assets	$ 316,885		314,706
Liabilities	291,880		288,506
VIE - primary beneficiary
Variable Interest Entity [Line Items]
Assets	13		17
Liabilities	0		4
Potential maximum loss exposure of unconsolidated funds	13
VIE - not primary beneficiary
Variable Interest Entity [Line Items]
Potential maximum loss exposure of unconsolidated funds	22
State and political subdivisions, securities in trusts
Variable Interest Entity [Line Items]
Investment securities related to state and political subdivisions	$ 700		$ 700