Variable Interest Entities (Details) - USD ($)	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018
Variable Interest Entity [Line Items]
Variable interest entity, other short-term borrowings	$ 820,000,000	$ 930,000,000
Weighted average life of trusts	3 years	3 years 7 months 6 days
Total standby bond purchase agreement committed to trusts	$ 823,000,000
VIE - primary beneficiary
Variable Interest Entity [Line Items]
Assets	21,000,000
Liabilities	5,000,000
Potential maximum loss exposure of unconsolidated funds	15,000,000	$ 0
VIE - not primary beneficiary
Variable Interest Entity [Line Items]
Potential maximum loss exposure of unconsolidated funds	41,000,000	70,000,000
State and political subdivisions, securities in trusts
Variable Interest Entity [Line Items]
Investment securities related to state and political subdivisions	$ 940,000,000	$ 1,050,000,000.00