Variable Interest Entities (Details) - USD ($)	Dec. 31, 2021	Dec. 31, 2020
Variable Interest Entity [Line Items]
Variable interest entity, other short-term borrowings		$ 620,000,000
Total standby bond purchase agreement committed to trusts	$ 0
Assets	314,624,000,000	314,706,000,000
Liabilities	287,261,000,000	288,506,000,000
VIE - primary beneficiary
Variable Interest Entity [Line Items]
Assets	0	17,000,000
Liabilities	0	4,000,000
Potential maximum loss exposure of unconsolidated funds		13,000,000
VIE - not primary beneficiary
Variable Interest Entity [Line Items]
Potential maximum loss exposure of unconsolidated funds	17,000,000	22,000,000
State and political subdivisions, securities in trusts
Variable Interest Entity [Line Items]
Investment securities related to state and political subdivisions	$ 520,000,000	$ 700,000,000