Commitments, Contingent Liabilities and Guarantees - Narrative (Details) $ in Millions	12 Months Ended
	Dec. 31, 2019 USD ($)
Commitments Contingencies And Guarantees [Line Items]
Default guarantees, value	$ 118
Written Put Options [Member]
Commitments Contingencies And Guarantees [Line Items]
Default guarantees, value	$ 32
Weighted average life of written put options	3 years
Standby Letters of Credit [Member]
Commitments Contingencies And Guarantees [Line Items]
Remaining weighted-average life of standby letters of credit in years	2 years
Default guarantees, value	$ 72
Underwriting And Servicing Program [Member]
Commitments Contingencies And Guarantees [Line Items]
Weighted-average remaining term for outstanding commercial mortgage loans in years	7 years 8 months 12 days
Unpaid principal balance outstanding of loans sold	$ 16,500
Maximum potential amount of undiscounted future payments that could be required, percentage of principal balance of loans outstanding	30.00%
Default guarantees, value	$ 7
Residential Mortgage Reserve [Member]
Commitments Contingencies And Guarantees [Line Items]
Unpaid principal balance outstanding of loans sold	$ 6,100
Maximum potential amount of undiscounted future payments that could be required, percentage of principal balance of loans outstanding	30.00%
Default guarantees, value	$ 7
Default Guarantees [Member]
Commitments Contingencies And Guarantees [Line Items]
Default guarantees, value	$ 1
Minimum [Member] | Standby Letters of Credit [Member]
Commitments Contingencies And Guarantees [Line Items]
Remaining actual life letters of credit in years	1 year
Minimum [Member] | Low [Member]
Commitments Contingencies And Guarantees [Line Items]
Guarantee obligations, probability of payment	0.00%
Minimum [Member] | Moderate [Member]
Commitments Contingencies And Guarantees [Line Items]
Guarantee obligations, probability of payment	30.00%
Minimum [Member] | High [Member]
Commitments Contingencies And Guarantees [Line Items]
Guarantee obligations, probability of payment	70.00%
Maximum [Member] | Standby Letters of Credit [Member]
Commitments Contingencies And Guarantees [Line Items]
Remaining actual life letters of credit in years	15 years
Maximum [Member] | Low [Member]
Commitments Contingencies And Guarantees [Line Items]
Guarantee obligations, probability of payment	30.00%
Maximum [Member] | Moderate [Member]
Commitments Contingencies And Guarantees [Line Items]
Guarantee obligations, probability of payment	70.00%