Derivatives and Hedging Activities - Credit Derivatives (Detail) - USD ($) $ in Millions	Sep. 30, 2020	Dec. 31, 2019
Derivative [Line Items]
Maximum Payout/Notional Amount of Written Credit Derivative	$ 558,186	$ 522,569
Maximum Payout/Notional Amount of Purchased Credit Derivatives	607,730	581,760
Offsetting Purchased Credit Derivatives [Member]
Derivative [Line Items]
Maximum Payout/Notional Amount of Purchased Credit Derivatives	489,782	426,100
Other Purchased Credit Derivatives [Member]
Derivative [Line Items]
Maximum Payout/Notional Amount of Purchased Credit Derivatives	117,946	155,662
Less than 1 Year [Member]
Derivative [Line Items]
Maximum Payout/Notional Amount of Written Credit Derivative	113,583	154,433
1 - 5 Years [Member]
Derivative [Line Items]
Maximum Payout/Notional Amount of Written Credit Derivative	351,113	316,786
Greater than 5 Years [Member]
Derivative [Line Items]
Maximum Payout/Notional Amount of Written Credit Derivative	93,490	51,350
Written Credit Derivative [Member]
Derivative [Line Items]
Fair Value Asset of Written Credit Derivatives	8,440	13,911
Fair Value Liability of Written Credit Derivatives	7,189	5,549
Fair Value Net Asset/(Liability) of Written Credit Derivatives	1,251	8,362
0 - 250 [Member]
Derivative [Line Items]
Maximum Payout/Notional Amount of Written Credit Derivative	474,877	484,119
0 - 250 [Member] | Offsetting Purchased Credit Derivatives [Member]
Derivative [Line Items]
Maximum Payout/Notional Amount of Purchased Credit Derivatives	421,367	395,127
0 - 250 [Member] | Other Purchased Credit Derivatives [Member]
Derivative [Line Items]
Maximum Payout/Notional Amount of Purchased Credit Derivatives	100,867	149,092
0 - 250 [Member] | Less than 1 Year [Member]
Derivative [Line Items]
Maximum Payout/Notional Amount of Written Credit Derivative	98,080	143,566
0 - 250 [Member] | 1 - 5 Years [Member]
Derivative [Line Items]
Maximum Payout/Notional Amount of Written Credit Derivative	296,222	292,444
0 - 250 [Member] | Greater than 5 Years [Member]
Derivative [Line Items]
Maximum Payout/Notional Amount of Written Credit Derivative	80,575	48,109
0 - 250 [Member] | Written Credit Derivative [Member]
Derivative [Line Items]
Fair Value Asset of Written Credit Derivatives	7,598	13,103
Fair Value Liability of Written Credit Derivatives	1,116	1,239
Fair Value Net Asset/(Liability) of Written Credit Derivatives	6,482	11,864
251 - 500 [Member]
Derivative [Line Items]
Maximum Payout/Notional Amount of Written Credit Derivative	43,693	19,540
251 - 500 [Member] | Offsetting Purchased Credit Derivatives [Member]
Derivative [Line Items]
Maximum Payout/Notional Amount of Purchased Credit Derivatives	33,354	14,492
251 - 500 [Member] | Other Purchased Credit Derivatives [Member]
Derivative [Line Items]
Maximum Payout/Notional Amount of Purchased Credit Derivatives	11,085	2,617
251 - 500 [Member] | Less than 1 Year [Member]
Derivative [Line Items]
Maximum Payout/Notional Amount of Written Credit Derivative	11,545	7,155
251 - 500 [Member] | 1 - 5 Years [Member]
Derivative [Line Items]
Maximum Payout/Notional Amount of Written Credit Derivative	25,444	10,125
251 - 500 [Member] | Greater than 5 Years [Member]
Derivative [Line Items]
Maximum Payout/Notional Amount of Written Credit Derivative	6,704	2,260
251 - 500 [Member] | Written Credit Derivative [Member]
Derivative [Line Items]
Fair Value Asset of Written Credit Derivatives	428	446
Fair Value Liability of Written Credit Derivatives	774	448
Fair Value Net Asset/(Liability) of Written Credit Derivatives	(346)	(2)
501 - 1000 [Member]
Derivative [Line Items]
Maximum Payout/Notional Amount of Written Credit Derivative	23,687	6,668
501 - 1000 [Member] | Offsetting Purchased Credit Derivatives [Member]
Derivative [Line Items]
Maximum Payout/Notional Amount of Purchased Credit Derivatives	20,018	5,938
501 - 1000 [Member] | Other Purchased Credit Derivatives [Member]
Derivative [Line Items]
Maximum Payout/Notional Amount of Purchased Credit Derivatives	3,932	1,599
501 - 1000 [Member] | Less than 1 Year [Member]
Derivative [Line Items]
Maximum Payout/Notional Amount of Written Credit Derivative	1,550	759
501 - 1000 [Member] | 1 - 5 Years [Member]
Derivative [Line Items]
Maximum Payout/Notional Amount of Written Credit Derivative	16,824	5,482
501 - 1000 [Member] | Greater than 5 Years [Member]
Derivative [Line Items]
Maximum Payout/Notional Amount of Written Credit Derivative	5,313	427
501 - 1000 [Member] | Written Credit Derivative [Member]
Derivative [Line Items]
Fair Value Asset of Written Credit Derivatives	243	160
Fair Value Liability of Written Credit Derivatives	1,942	372
Fair Value Net Asset/(Liability) of Written Credit Derivatives	(1,699)	(212)
Greater than 1000 [Member]
Derivative [Line Items]
Maximum Payout/Notional Amount of Written Credit Derivative	15,929	12,242
Greater than 1000 [Member] | Offsetting Purchased Credit Derivatives [Member]
Derivative [Line Items]
Maximum Payout/Notional Amount of Purchased Credit Derivatives	15,043	10,543
Greater than 1000 [Member] | Other Purchased Credit Derivatives [Member]
Derivative [Line Items]
Maximum Payout/Notional Amount of Purchased Credit Derivatives	2,062	2,354
Greater than 1000 [Member] | Less than 1 Year [Member]
Derivative [Line Items]
Maximum Payout/Notional Amount of Written Credit Derivative	2,408	2,953
Greater than 1000 [Member] | 1 - 5 Years [Member]
Derivative [Line Items]
Maximum Payout/Notional Amount of Written Credit Derivative	12,623	8,735
Greater than 1000 [Member] | Greater than 5 Years [Member]
Derivative [Line Items]
Maximum Payout/Notional Amount of Written Credit Derivative	898	554
Greater than 1000 [Member] | Written Credit Derivative [Member]
Derivative [Line Items]
Fair Value Asset of Written Credit Derivatives	171	202
Fair Value Liability of Written Credit Derivatives	3,357	3,490
Fair Value Net Asset/(Liability) of Written Credit Derivatives	$ (3,186)	$ (3,288)