Derivative Instruments - Asset and Liability Management Derivative Positions of Company (Detail) - Asset and Liability Management Positions [Member] - USD ($) $ in Millions		9 Months Ended	12 Months Ended
		Sep. 30, 2020	Dec. 31, 2019
Derivative [Line Items]
Notional Value, Assets		$ 46,812	$ 58,966
Fair Value, Assets		390	142
Notional Value, Liabilities		61,169	42,288
Fair Value, Liabilities		553	301
Other Derivatives [Member]
Derivative [Line Items]
Notional Value, Assets	[1]	588	$ 34
Fair Value, Assets	[1]	$ 4
Derivative Asset Average Remaining Maturity Period	[1]	7 days	3 days
Notional Value, Liabilities	[1]	$ 2,376	$ 1,823
Fair Value, Liabilities	[1]	$ 199	$ 165
Derivative Liability Average Remaining Maturity Period	[1]	2 years 25 days	2 years 5 months 12 days
Other Economic Hedges [Member] | Interest Rate Contracts [Member] | Receive Fixed/Pay Floating Swaps [Member]
Derivative [Line Items]
Notional Value, Assets		$ 4,985	$ 4,408
Derivative Asset Average Remaining Maturity Period		5 years 4 months 9 days	5 years 11 months 26 days
Notional Value, Liabilities		$ 6,367	$ 5,316
Derivative Liability Average Remaining Maturity Period		11 years 2 months 4 days	13 years 14 days
Other Economic Hedges [Member] | Interest Rate Contracts [Member] | Pay Fixed/Receive Floating Swaps [Member]
Derivative [Line Items]
Notional Value, Assets		$ 604	$ 1,259
Derivative Asset Average Remaining Maturity Period		10 years 6 months 18 days	5 years 8 months 1 day
Notional Value, Liabilities		$ 6,207	$ 4,497
Derivative Liability Average Remaining Maturity Period		4 years 3 months 21 days	6 years 10 days
Other Economic Hedges [Member] | Interest Rate Contracts [Member] | Futures and Forwards [Member] | Purchased [Member]
Derivative [Line Items]
Notional Value, Assets		$ 13,858	$ 5,409
Fair Value, Assets		$ 88	$ 17
Derivative Asset Average Remaining Maturity Period		21 days	29 days
Notional Value, Liabilities		$ 5,141	$ 5,477
Fair Value, Liabilities		$ 11	$ 11
Derivative Liability Average Remaining Maturity Period		4 months 28 days	25 days
Other Economic Hedges [Member] | Interest Rate Contracts [Member] | Futures and Forwards [Member] | Written [Member]
Derivative [Line Items]
Notional Value, Assets		$ 9,105	$ 16,333
Fair Value, Assets		$ 20	$ 13
Derivative Asset Average Remaining Maturity Period		14 days	9 months 21 days
Notional Value, Liabilities		$ 28,066	$ 8,113
Fair Value, Liabilities		$ 102	$ 25
Derivative Liability Average Remaining Maturity Period		1 month 28 days	10 days
Other Economic Hedges [Member] | Interest Rate Contracts [Member] | Options [Member] | Purchased [Member]
Derivative [Line Items]
Notional Value, Assets		$ 2,570	$ 10,180
Fair Value, Assets		$ 44	$ 79
Derivative Asset Average Remaining Maturity Period		4 years 10 months 28 days	2 years 11 months 19 days
Notional Value, Liabilities		$ 1,340
Derivative Liability Average Remaining Maturity Period		4 years 3 months
Other Economic Hedges [Member] | Interest Rate Contracts [Member] | Options [Member] | Written [Member]
Derivative [Line Items]
Notional Value, Assets		$ 5,817	$ 1,270
Fair Value, Assets		$ 227	$ 30
Derivative Asset Average Remaining Maturity Period		1 month 9 days	29 days
Notional Value, Liabilities		$ 7,800	$ 4,238
Fair Value, Liabilities		$ 227	$ 81
Derivative Liability Average Remaining Maturity Period		2 years 9 months 25 days	2 years 25 days
Other Economic Hedges [Member] | Foreign Exchange Forward Contracts [Member]
Derivative [Line Items]
Notional Value, Assets		$ 275	$ 113
Fair Value, Assets		$ 2	$ 1
Derivative Asset Average Remaining Maturity Period		14 days	18 days
Notional Value, Liabilities		$ 294	$ 467
Fair Value, Liabilities		$ 2	$ 6
Derivative Liability Average Remaining Maturity Period		18 days	14 days
Other Economic Hedges [Member] | Equity Contracts [Member]
Derivative [Line Items]
Notional Value, Assets		$ 127	$ 128
Fair Value, Assets			$ 2
Derivative Asset Average Remaining Maturity Period		8 months 1 day	5 months 12 days
Notional Value, Liabilities		$ 20	$ 20
Derivative Liability Average Remaining Maturity Period		7 months 20 days	1 year 21 days
Fair Value Hedges [Member] | Interest Rate Contracts [Member] | Receive Fixed/Pay Floating Swaps [Member]
Derivative [Line Items]
Notional Value, Assets		$ 8,400	$ 18,300
Derivative Asset Average Remaining Maturity Period		2 years 7 days	3 years 10 months 20 days
Notional Value, Liabilities			$ 4,900
Derivative Liability Average Remaining Maturity Period			3 years 5 months 26 days
Cash Flow Hedges [Member] | Interest Rate Contracts [Member] | Pay Fixed/Receive Floating Swaps [Member]
Derivative [Line Items]
Notional Value, Assets			$ 1,532
Derivative Asset Average Remaining Maturity Period			6 years 21 days
Notional Value, Liabilities		$ 3,250	$ 7,150
Fair Value, Liabilities		$ 11	$ 10
Derivative Liability Average Remaining Maturity Period		4 years 10 months 2 days	2 years 1 month 9 days
Net Investment Hedges [Member] | Foreign Exchange Forward Contracts [Member]
Derivative [Line Items]
Notional Value, Assets		$ 483
Fair Value, Assets		$ 5
Derivative Asset Average Remaining Maturity Period		21 days
Notional Value, Liabilities		$ 308	$ 287
Fair Value, Liabilities		$ 1	$ 3
Derivative Liability Average Remaining Maturity Period		21 days	14 days

[1] Includes derivative liability swap agreements related to the sale of a portion of the Company’s Class B common and preferred shares of Visa Inc. The Visa swap agreements had a total notional value, fair value and weighted-average remaining maturity of $1.8 billion, $195 million and 2.75 years at September 30, 2020, respectively, compared to $1.8 billion, $165 million and 2.50 years at December 31, 2019, respectively. In addition, includes short-term underwriting purchase and sale commitments with total asset and liability notional values of $588 million at September 30, 2020, and $34 million at December 31, 2019.