Loans - Summary of Concentration of Secured and Unsecured Loans (Detail) - USD ($) $ in Millions	9 Months Ended	12 Months Ended
	Sep. 30, 2020	Dec. 31, 2019
Financing Receivable, Recorded Investment [Line Items]
Loans and Leases Receivable, Gross	$ 115,557	$ 110,345
Concentration Risk,Percentage	100.00%	100.00%
Loans receivable at fair value	$ 13,881	$ 14,386
Corporate [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans and Leases Receivable, Gross	$ 51,465	$ 46,307
Concentration Risk,Percentage	100.00%	100.00%
Loans receivable at fair value	$ 2,856	$ 3,224
Wealth management [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans and Leases Receivable, Gross	$ 29,836	$ 27,940
Concentration Risk,Percentage	100.00%	100.00%
Loans receivable at fair value	$ 8,037	$ 7,824
Commercial real estate [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans and Leases Receivable, Gross	$ 18,377	$ 17,743
Concentration Risk,Percentage	100.00%	100.00%
Loans receivable at fair value	$ 1,980	$ 1,876
Residential real estate [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans and Leases Receivable, Gross	$ 4,705	$ 6,958
Concentration Risk,Percentage	100.00%	100.00%
Loans receivable at fair value	$ 446	$ 792
Installment [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans and Leases Receivable, Gross	$ 4,112	$ 4,747
Concentration Risk,Percentage	100.00%	100.00%
Credit Card Receivable [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans and Leases Receivable, Gross	$ 2,908	$ 1,858
Concentration Risk,Percentage	100.00%	100.00%
Other [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans and Leases Receivable, Gross	$ 4,154	$ 4,792
Concentration Risk,Percentage	100.00%	100.00%
Loans receivable at fair value	$ 562	$ 670
Internally rated loans [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans and Leases Receivable, Gross	$ 115,557	$ 110,345
Concentration Risk,Percentage	100.00%	100.00%
Internally rated loans [Member] | Corporate [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans and Leases Receivable, Gross	$ 51,465	$ 46,307
Internally rated loans [Member] | Wealth management [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans and Leases Receivable, Gross	29,836	27,940
Internally rated loans [Member] | Commercial real estate [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans and Leases Receivable, Gross	18,377	17,743
Internally rated loans [Member] | Residential real estate [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans and Leases Receivable, Gross	4,705	6,958
Internally rated loans [Member] | Installment [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans and Leases Receivable, Gross	4,112	4,747
Internally rated loans [Member] | Credit Card Receivable [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans and Leases Receivable, Gross	2,908	1,858
Internally rated loans [Member] | Other [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans and Leases Receivable, Gross	$ 4,154	$ 4,792
Secured Loans [Member] | Internally rated loans [Member]
Financing Receivable, Recorded Investment [Line Items]
Concentration Risk,Percentage	81.00%	83.00%
Unsecured Loans [Member] | Internally rated loans [Member]
Financing Receivable, Recorded Investment [Line Items]
Concentration Risk,Percentage	19.00%	17.00%
Amortized cost [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans and Leases Receivable, Gross	$ 99,170	$ 90,636
Loans receivable at fair value	96,615	89,186
Amortized cost [Member] | Corporate [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans and Leases Receivable, Gross	47,583	41,129
Amortized cost [Member] | Wealth management [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans and Leases Receivable, Gross	21,799	20,116
Amortized cost [Member] | Commercial real estate [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans and Leases Receivable, Gross	15,421	13,258
Amortized cost [Member] | Residential real estate [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans and Leases Receivable, Gross	4,236	6,132
Amortized cost [Member] | Credit Card Receivable [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans and Leases Receivable, Gross	2,908	1,858
Amortized cost [Member] | Other [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans and Leases Receivable, Gross	3,111	3,396
Fair Value [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans receivable at fair value	13,881	14,386
Fair Value [Member] | Corporate [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans receivable at fair value	2,856	3,224
Fair Value [Member] | Wealth management [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans receivable at fair value	8,037	7,824
Fair Value [Member] | Commercial real estate [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans receivable at fair value	1,980	1,876
Fair Value [Member] | Residential real estate [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans receivable at fair value	446	792
Fair Value [Member] | Other [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans receivable at fair value	562	670
Fair Value [Member] | Internally rated loans [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans receivable at fair value	13,881	14,386
Held for sale [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans Receivable Held-for-sale, Amount	2,506	5,323
Loans receivable at fair value	2,513	5,409
Held for sale [Member] | Corporate [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans Receivable Held-for-sale, Amount	1,026	1,954
Held for sale [Member] | Commercial real estate [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans Receivable Held-for-sale, Amount	976	2,609
Held for sale [Member] | Residential real estate [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans Receivable Held-for-sale, Amount	23	34
Held for sale [Member] | Other [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans Receivable Held-for-sale, Amount	481	726
Held for sale [Member] | Internally rated loans [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans Receivable Held-for-sale, Amount	2,506	5,323
Loans Receivable [Member] | Amortized cost [Member] | Internally rated loans [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans and Leases Receivable, Gross	99,170	90,636
Loans Receivable [Member] | Investment-Grade [Member] | Internally rated loans [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans and Leases Receivable, Gross	$ 34,021	$ 33,433
Concentration Risk,Percentage	100.00%	100.00%
Loans Receivable [Member] | Investment-Grade [Member] | Internally rated loans [Member] | Corporate [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans and Leases Receivable, Gross	$ 10,880	$ 10,507
Loans Receivable [Member] | Investment-Grade [Member] | Internally rated loans [Member] | Wealth management [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans and Leases Receivable, Gross	19,333	20,001
Loans Receivable [Member] | Investment-Grade [Member] | Internally rated loans [Member] | Commercial real estate [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans and Leases Receivable, Gross	1,468	306
Loans Receivable [Member] | Investment-Grade [Member] | Internally rated loans [Member] | Residential real estate [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans and Leases Receivable, Gross	689	244
Loans Receivable [Member] | Investment-Grade [Member] | Internally rated loans [Member] | Other [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans and Leases Receivable, Gross	$ 1,651	$ 2,375
Loans Receivable [Member] | Investment-Grade [Member] | Secured Loans [Member] | Internally rated loans [Member]
Financing Receivable, Recorded Investment [Line Items]
Concentration Risk,Percentage	79.00%	83.00%
Loans Receivable [Member] | Investment-Grade [Member] | Unsecured Loans [Member] | Internally rated loans [Member]
Financing Receivable, Recorded Investment [Line Items]
Concentration Risk,Percentage	21.00%	17.00%
Loans Receivable [Member] | Investment-Grade [Member] | Amortized cost [Member] | Internally rated loans [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans and Leases Receivable, Gross	$ 31,487	$ 30,266
Loans Receivable [Member] | Investment-Grade [Member] | Fair Value [Member] | Internally rated loans [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans receivable at fair value	2,068	2,844
Loans Receivable [Member] | Investment-Grade [Member] | Held for sale [Member] | Internally rated loans [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans Receivable Held-for-sale, Amount	466	323
Loans Receivable [Member] | Non-Investment-Grade [Member] | Internally rated loans [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans and Leases Receivable, Gross	$ 64,595	$ 60,764
Concentration Risk,Percentage	100.00%	100.00%
Loans Receivable [Member] | Non-Investment-Grade [Member] | Internally rated loans [Member] | Corporate [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans and Leases Receivable, Gross	$ 39,972	$ 35,509
Loans Receivable [Member] | Non-Investment-Grade [Member] | Internally rated loans [Member] | Wealth management [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans and Leases Receivable, Gross	4,923	3,576
Loans Receivable [Member] | Non-Investment-Grade [Member] | Internally rated loans [Member] | Commercial real estate [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans and Leases Receivable, Gross	15,922	15,997
Loans Receivable [Member] | Non-Investment-Grade [Member] | Internally rated loans [Member] | Residential real estate [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans and Leases Receivable, Gross	2,796	4,600
Loans Receivable [Member] | Non-Investment-Grade [Member] | Internally rated loans [Member] | Other [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans and Leases Receivable, Gross	$ 982	$ 1,082
Loans Receivable [Member] | Non-Investment-Grade [Member] | Secured Loans [Member] | Internally rated loans [Member]
Financing Receivable, Recorded Investment [Line Items]
Concentration Risk,Percentage	91.00%	91.00%
Loans Receivable [Member] | Non-Investment-Grade [Member] | Unsecured Loans [Member] | Internally rated loans [Member]
Financing Receivable, Recorded Investment [Line Items]
Concentration Risk,Percentage	9.00%	9.00%
Loans Receivable [Member] | Non-Investment-Grade [Member] | Amortized cost [Member] | Internally rated loans [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans and Leases Receivable, Gross	$ 57,168	$ 51,222
Loans Receivable [Member] | Non-Investment-Grade [Member] | Fair Value [Member] | Internally rated loans [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans receivable at fair value	5,863	5,174
Loans Receivable [Member] | Non-Investment-Grade [Member] | Held for sale [Member] | Internally rated loans [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans Receivable Held-for-sale, Amount	1,564	4,368
Loans Receivable [Member] | Unrated/Other [Member] | Internally rated loans [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans and Leases Receivable, Gross	$ 16,941	$ 16,148
Concentration Risk,Percentage	100.00%	100.00%
Loans Receivable [Member] | Unrated/Other [Member] | Internally rated loans [Member] | Corporate [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans and Leases Receivable, Gross	$ 613	$ 291
Loans Receivable [Member] | Unrated/Other [Member] | Internally rated loans [Member] | Wealth management [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans and Leases Receivable, Gross	5,580	4,363
Loans Receivable [Member] | Unrated/Other [Member] | Internally rated loans [Member] | Commercial real estate [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans and Leases Receivable, Gross	987	1,440
Loans Receivable [Member] | Unrated/Other [Member] | Internally rated loans [Member] | Residential real estate [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans and Leases Receivable, Gross	1,220	2,114
Loans Receivable [Member] | Unrated/Other [Member] | Internally rated loans [Member] | Installment [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans and Leases Receivable, Gross	4,112	4,747
Loans Receivable [Member] | Unrated/Other [Member] | Internally rated loans [Member] | Credit Card Receivable [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans and Leases Receivable, Gross	2,908	1,858
Loans Receivable [Member] | Unrated/Other [Member] | Internally rated loans [Member] | Other [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans and Leases Receivable, Gross	$ 1,521	$ 1,335
Loans Receivable [Member] | Unrated/Other [Member] | Secured Loans [Member] | Internally rated loans [Member]
Financing Receivable, Recorded Investment [Line Items]
Concentration Risk,Percentage	48.00%	54.00%
Loans Receivable [Member] | Unrated/Other [Member] | Unsecured Loans [Member] | Internally rated loans [Member]
Financing Receivable, Recorded Investment [Line Items]
Concentration Risk,Percentage	52.00%	46.00%
Loans Receivable [Member] | Unrated/Other [Member] | Amortized cost [Member] | Internally rated loans [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans and Leases Receivable, Gross	$ 10,515	$ 9,148
Loans Receivable [Member] | Unrated/Other [Member] | Fair Value [Member] | Internally rated loans [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans receivable at fair value	5,950	6,368
Loans Receivable [Member] | Unrated/Other [Member] | Held for sale [Member] | Internally rated loans [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans Receivable Held-for-sale, Amount	$ 476	$ 632