Derivatives and Hedging Activities - Credit Derivatives (Detail) - USD ($) $ in Millions	Dec. 31, 2019	Dec. 31, 2018
Derivative [Line Items]
Maximum Payout/Notional Amount of Written Credit Derivative	$ 522,569	$ 554,172
Maximum Payout/Notional Amount of Purchased Credit Derivatives	581,760	603,000
Offsetting Purchased Credit Derivatives [Member]
Derivative [Line Items]
Maximum Payout/Notional Amount of Purchased Credit Derivatives	426,100	461,902
Other Purchased Credit Derivatives [Member]
Derivative [Line Items]
Maximum Payout/Notional Amount of Purchased Credit Derivatives	155,662	141,095
Less than 1 Year [Member]
Derivative [Line Items]
Maximum Payout/Notional Amount of Written Credit Derivative	154,433	160,590
1 - 5 Years [Member]
Derivative [Line Items]
Maximum Payout/Notional Amount of Written Credit Derivative	316,786	340,683
Greater than 5 Years [Member]
Derivative [Line Items]
Maximum Payout/Notional Amount of Written Credit Derivative	51,350	52,899
Written Credit Derivative [Member]
Derivative [Line Items]
Fair Value Asset of Written Credit Derivatives	13,911	9,374
Fair Value Liability of Written Credit Derivatives	5,549	7,972
Fair Value Net Asset/(Liability) of Written Credit Derivatives	8,362	1,402
0 - 250 [Member]
Derivative [Line Items]
Maximum Payout/Notional Amount of Written Credit Derivative	484,119	489,746
0 - 250 [Member] | Offsetting Purchased Credit Derivatives [Member]
Derivative [Line Items]
Maximum Payout/Notional Amount of Purchased Credit Derivatives	395,127	413,445
0 - 250 [Member] | Other Purchased Credit Derivatives [Member]
Derivative [Line Items]
Maximum Payout/Notional Amount of Purchased Credit Derivatives	149,092	115,754
0 - 250 [Member] | Less than 1 Year [Member]
Derivative [Line Items]
Maximum Payout/Notional Amount of Written Credit Derivative	143,566	145,828
0 - 250 [Member] | 1 - 5 Years [Member]
Derivative [Line Items]
Maximum Payout/Notional Amount of Written Credit Derivative	292,444	298,228
0 - 250 [Member] | Greater than 5 Years [Member]
Derivative [Line Items]
Maximum Payout/Notional Amount of Written Credit Derivative	48,109	45,690
0 - 250 [Member] | Written Credit Derivative [Member]
Derivative [Line Items]
Fair Value Asset of Written Credit Derivatives	13,103	8,656
Fair Value Liability of Written Credit Derivatives	1,239	1,990
Fair Value Net Asset/(Liability) of Written Credit Derivatives	11,864	6,666
251 - 500 [Member]
Derivative [Line Items]
Maximum Payout/Notional Amount of Written Credit Derivative	19,540	36,829
251 - 500 [Member] | Offsetting Purchased Credit Derivatives [Member]
Derivative [Line Items]
Maximum Payout/Notional Amount of Purchased Credit Derivatives	14,492	25,373
251 - 500 [Member] | Other Purchased Credit Derivatives [Member]
Derivative [Line Items]
Maximum Payout/Notional Amount of Purchased Credit Derivatives	2,617	14,273
251 - 500 [Member] | Less than 1 Year [Member]
Derivative [Line Items]
Maximum Payout/Notional Amount of Written Credit Derivative	7,155	9,763
251 - 500 [Member] | 1 - 5 Years [Member]
Derivative [Line Items]
Maximum Payout/Notional Amount of Written Credit Derivative	10,125	21,100
251 - 500 [Member] | Greater than 5 Years [Member]
Derivative [Line Items]
Maximum Payout/Notional Amount of Written Credit Derivative	2,260	5,966
251 - 500 [Member] | Written Credit Derivative [Member]
Derivative [Line Items]
Fair Value Asset of Written Credit Derivatives	446	543
Fair Value Liability of Written Credit Derivatives	448	1,415
Fair Value Net Asset/(Liability) of Written Credit Derivatives	(2)	(872)
501 - 1000 [Member]
Derivative [Line Items]
Maximum Payout/Notional Amount of Written Credit Derivative	6,668	16,107
501 - 1000 [Member] | Offsetting Purchased Credit Derivatives [Member]
Derivative [Line Items]
Maximum Payout/Notional Amount of Purchased Credit Derivatives	5,938	14,243
501 - 1000 [Member] | Other Purchased Credit Derivatives [Member]
Derivative [Line Items]
Maximum Payout/Notional Amount of Purchased Credit Derivatives	1,599	7,555
501 - 1000 [Member] | Less than 1 Year [Member]
Derivative [Line Items]
Maximum Payout/Notional Amount of Written Credit Derivative	759	1,151
501 - 1000 [Member] | 1 - 5 Years [Member]
Derivative [Line Items]
Maximum Payout/Notional Amount of Written Credit Derivative	5,482	13,835
501 - 1000 [Member] | Greater than 5 Years [Member]
Derivative [Line Items]
Maximum Payout/Notional Amount of Written Credit Derivative	427	1,121
501 - 1000 [Member] | Written Credit Derivative [Member]
Derivative [Line Items]
Fair Value Asset of Written Credit Derivatives	160	95
Fair Value Liability of Written Credit Derivatives	372	1,199
Fair Value Net Asset/(Liability) of Written Credit Derivatives	(212)	(1,104)
Greater than 1000 [Member]
Derivative [Line Items]
Maximum Payout/Notional Amount of Written Credit Derivative	12,242	11,490
Greater than 1000 [Member] | Offsetting Purchased Credit Derivatives [Member]
Derivative [Line Items]
Maximum Payout/Notional Amount of Purchased Credit Derivatives	10,543	8,841
Greater than 1000 [Member] | Other Purchased Credit Derivatives [Member]
Derivative [Line Items]
Maximum Payout/Notional Amount of Purchased Credit Derivatives	2,354	3,513
Greater than 1000 [Member] | Less than 1 Year [Member]
Derivative [Line Items]
Maximum Payout/Notional Amount of Written Credit Derivative	2,953	3,848
Greater than 1000 [Member] | 1 - 5 Years [Member]
Derivative [Line Items]
Maximum Payout/Notional Amount of Written Credit Derivative	8,735	7,520
Greater than 1000 [Member] | Greater than 5 Years [Member]
Derivative [Line Items]
Maximum Payout/Notional Amount of Written Credit Derivative	554	122
Greater than 1000 [Member] | Written Credit Derivative [Member]
Derivative [Line Items]
Fair Value Asset of Written Credit Derivatives	202	80
Fair Value Liability of Written Credit Derivatives	3,490	3,368
Fair Value Net Asset/(Liability) of Written Credit Derivatives	$ (3,288)	$ (3,288)