Derivatives and Hedging Activities - Additional Information (Details) $ in Millions	9 Months Ended
	Sep. 30, 2020 USD ($) rating derivative	Dec. 31, 2019 USD ($) rating
Credit Derivatives [Line Items]
Derivative assets after effects of bilateral collateral and master netting agreements	$ 105
Derivative liabilities after effects of bilateral collateral and master netting agreements	2
Derivative assets not designated as hedging instruments after effects of bilateral collateral and master netting agreements, and a reserve for potential future losses	1,800
Derivative liabilities not designated as hedging instruments after effects of bilateral collateral and master netting agreements, and a reserve for potential future losses	166
Reclassify of after-tax net gains on derivative instruments from AOCI	$ 253
Length of time hedge in cash flow hedge	12 months
Reclassification of net losses related to terminated cash flow hedges from AOCI to income	$ 74
Maximum length of time over which forecasted transactions are hedged, years	9 years
Cash collateral netted against derivative assets	$ 44	$ 207
Collateral netted against derivative liabilities	234	69
Gross exposure on derivatives, after taking into account the effects of bilateral collateral and master netting agreements	411
Net exposure on derivatives, after taking into account, the effects of bilateral collateral and master netting agreements	260
Over-collateralization on derivatives to broker-dealers and banks, after the application of master netting agreements and collateral	257
Additional collateral held in the form of securities	3
Default reserve associated with uncollateralized contracts	72
Gross exposure on derivatives after taking into account effects of master netting agreements	1,900
Net exposure on derivatives with clients after application of master netting agreements collateral and related reserve	1,700
Net liability position totaled	12	$ 9
Banking Subsidiary
Credit Derivatives [Line Items]
Net liability position totaled	177
Derivative assets included in net liability position	108
Derivative liabilities included in net liability position	285
Cash and securities collateral posted	$ 175
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)	$ 3	$ 3