Derivatives and Hedging Activities - Additional Information (Details) $ in Millions	9 Months Ended
	Sep. 30, 2021 USD ($) derivative rating	Dec. 31, 2020 USD ($) rating
Credit Derivatives [Line Items]
Derivative assets after effects of bilateral collateral and master netting agreements	$ 84
Derivative liabilities after effects of bilateral collateral and master netting agreements	11
Derivative assets not designated as hedging instruments after effects of bilateral collateral and master netting agreements, and a reserve for potential future losses	2,500
Derivative liabilities not designated as hedging instruments after effects of bilateral collateral and master netting agreements, and a reserve for potential future losses	249
Reclassify of after-tax net gains on derivative instruments from AOCI	$ 167
Length of time hedge in cash flow hedge	12 months
Reclassification of net losses related to terminated cash flow hedges from AOCI to income	$ 6
Maximum length of time over which forecasted transactions are hedged, years	5 years 10 months 24 days
Cash collateral netted against derivative assets	$ 49	$ 63
Collateral netted against derivative liabilities	1,600	232
Gross exposure on derivatives, after taking into account the effects of bilateral collateral and master netting agreements	159
Net exposure on derivatives, after taking into account, the effects of bilateral collateral and master netting agreements	175
Over-collateralization on derivatives to broker-dealers and banks, after the application of master netting agreements and collateral	173
Additional collateral held in the form of securities	2
Default reserve associated with uncollateralized contracts	25
Gross exposure on derivatives after taking into account effects of master netting agreements	2,500
Net exposure on derivatives with clients after application of master netting agreements collateral and related reserve	2,400
Net liability position totaled	7	$ 9
Banking Subsidiary
Credit Derivatives [Line Items]
Net liability position totaled	1,700
Derivative assets included in net liability position	194
Derivative liabilities included in net liability position	1,900
Cash and securities collateral posted	$ 1,600
Number of credit risk derivatives held | derivative	0
Banking Subsidiary | Unsecured Debt
Credit Derivatives [Line Items]
Number of ratings above noninvestment | rating	4	4
Banking Subsidiary | Maximum | Unsecured Debt
Credit Derivatives [Line Items]
Payments to terminate contracts (less than for the $1 million)	$ 4	$ 2