Derivatives and Hedging Activities - Credit Derivatives (Detail) - USD ($) $ in Millions	Mar. 31, 2020	Dec. 31, 2019
Derivative [Line Items]
Maximum Payout/Notional Amount of Written Credit Derivative	$ 657,117	$ 522,569
Maximum Payout/Notional Amount of Purchased Credit Derivatives	705,200	581,760
Offsetting Purchased Credit Derivatives [Member]
Derivative [Line Items]
Maximum Payout/Notional Amount of Purchased Credit Derivatives	553,358	426,100
Other Purchased Credit Derivatives [Member]
Derivative [Line Items]
Maximum Payout/Notional Amount of Purchased Credit Derivatives	151,843	155,662
Less than 1 Year [Member]
Derivative [Line Items]
Maximum Payout/Notional Amount of Written Credit Derivative	193,333	154,433
1 - 5 Years [Member]
Derivative [Line Items]
Maximum Payout/Notional Amount of Written Credit Derivative	362,650	316,786
Greater than 5 Years [Member]
Derivative [Line Items]
Maximum Payout/Notional Amount of Written Credit Derivative	101,134	51,350
Written Credit Derivative [Member]
Derivative [Line Items]
Fair Value Asset of Written Credit Derivatives	4,160	13,911
Fair Value Liability of Written Credit Derivatives	17,813	5,549
Fair Value Net Asset/(Liability) of Written Credit Derivatives	(13,653)	8,362
0 - 250 [Member]
Derivative [Line Items]
Maximum Payout/Notional Amount of Written Credit Derivative	562,329	484,119
0 - 250 [Member] | Offsetting Purchased Credit Derivatives [Member]
Derivative [Line Items]
Maximum Payout/Notional Amount of Purchased Credit Derivatives	476,787	395,127
0 - 250 [Member] | Other Purchased Credit Derivatives [Member]
Derivative [Line Items]
Maximum Payout/Notional Amount of Purchased Credit Derivatives	127,244	149,092
0 - 250 [Member] | Less than 1 Year [Member]
Derivative [Line Items]
Maximum Payout/Notional Amount of Written Credit Derivative	167,856	143,566
0 - 250 [Member] | 1 - 5 Years [Member]
Derivative [Line Items]
Maximum Payout/Notional Amount of Written Credit Derivative	303,456	292,444
0 - 250 [Member] | Greater than 5 Years [Member]
Derivative [Line Items]
Maximum Payout/Notional Amount of Written Credit Derivative	91,017	48,109
0 - 250 [Member] | Written Credit Derivative [Member]
Derivative [Line Items]
Fair Value Asset of Written Credit Derivatives	3,833	13,103
Fair Value Liability of Written Credit Derivatives	4,333	1,239
Fair Value Net Asset/(Liability) of Written Credit Derivatives	(500)	11,864
251 - 500 [Member]
Derivative [Line Items]
Maximum Payout/Notional Amount of Written Credit Derivative	34,360	19,540
251 - 500 [Member] | Offsetting Purchased Credit Derivatives [Member]
Derivative [Line Items]
Maximum Payout/Notional Amount of Purchased Credit Derivatives	29,983	14,492
251 - 500 [Member] | Other Purchased Credit Derivatives [Member]
Derivative [Line Items]
Maximum Payout/Notional Amount of Purchased Credit Derivatives	6,841	2,617
251 - 500 [Member] | Less than 1 Year [Member]
Derivative [Line Items]
Maximum Payout/Notional Amount of Written Credit Derivative	3,283	7,155
251 - 500 [Member] | 1 - 5 Years [Member]
Derivative [Line Items]
Maximum Payout/Notional Amount of Written Credit Derivative	25,507	10,125
251 - 500 [Member] | Greater than 5 Years [Member]
Derivative [Line Items]
Maximum Payout/Notional Amount of Written Credit Derivative	5,570	2,260
251 - 500 [Member] | Written Credit Derivative [Member]
Derivative [Line Items]
Fair Value Asset of Written Credit Derivatives	246	446
Fair Value Liability of Written Credit Derivatives	1,939	448
Fair Value Net Asset/(Liability) of Written Credit Derivatives	(1,693)	(2)
501 - 1000 [Member]
Derivative [Line Items]
Maximum Payout/Notional Amount of Written Credit Derivative	36,691	6,668
501 - 1000 [Member] | Offsetting Purchased Credit Derivatives [Member]
Derivative [Line Items]
Maximum Payout/Notional Amount of Purchased Credit Derivatives	24,949	5,938
501 - 1000 [Member] | Other Purchased Credit Derivatives [Member]
Derivative [Line Items]
Maximum Payout/Notional Amount of Purchased Credit Derivatives	12,957	1,599
501 - 1000 [Member] | Less than 1 Year [Member]
Derivative [Line Items]
Maximum Payout/Notional Amount of Written Credit Derivative	17,312	759
501 - 1000 [Member] | 1 - 5 Years [Member]
Derivative [Line Items]
Maximum Payout/Notional Amount of Written Credit Derivative	16,341	5,482
501 - 1000 [Member] | Greater than 5 Years [Member]
Derivative [Line Items]
Maximum Payout/Notional Amount of Written Credit Derivative	3,038	427
501 - 1000 [Member] | Written Credit Derivative [Member]
Derivative [Line Items]
Fair Value Asset of Written Credit Derivatives	30	160
Fair Value Liability of Written Credit Derivatives	3,304	372
Fair Value Net Asset/(Liability) of Written Credit Derivatives	(3,274)	(212)
Greater than 1000 [Member]
Derivative [Line Items]
Maximum Payout/Notional Amount of Written Credit Derivative	23,737	12,242
Greater than 1000 [Member] | Offsetting Purchased Credit Derivatives [Member]
Derivative [Line Items]
Maximum Payout/Notional Amount of Purchased Credit Derivatives	21,639	10,543
Greater than 1000 [Member] | Other Purchased Credit Derivatives [Member]
Derivative [Line Items]
Maximum Payout/Notional Amount of Purchased Credit Derivatives	4,801	2,354
Greater than 1000 [Member] | Less than 1 Year [Member]
Derivative [Line Items]
Maximum Payout/Notional Amount of Written Credit Derivative	4,882	2,953
Greater than 1000 [Member] | 1 - 5 Years [Member]
Derivative [Line Items]
Maximum Payout/Notional Amount of Written Credit Derivative	17,346	8,735
Greater than 1000 [Member] | Greater than 5 Years [Member]
Derivative [Line Items]
Maximum Payout/Notional Amount of Written Credit Derivative	1,509	554
Greater than 1000 [Member] | Written Credit Derivative [Member]
Derivative [Line Items]
Fair Value Asset of Written Credit Derivatives	51	202
Fair Value Liability of Written Credit Derivatives	8,237	3,490
Fair Value Net Asset/(Liability) of Written Credit Derivatives	$ (8,186)	$ (3,288)