Loans - Summary of Concentration of Secured and Unsecured Loans (Detail) - USD ($) $ in Millions	3 Months Ended	12 Months Ended
	Mar. 31, 2020	Dec. 31, 2019
Financing Receivable, Recorded Investment [Line Items]
Loans and Leases Receivable, Gross	$ 131,321	$ 110,345
Concentration Risk,Percentage	100.00%	100.00%
Loans receivable at fair value	$ 13,829	$ 14,386
Corporate [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans and Leases Receivable, Gross	$ 68,530	$ 46,307
Concentration Risk,Percentage	100.00%	100.00%
Loans receivable at fair value	$ 2,915	$ 3,224
Wealth management [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans and Leases Receivable, Gross	$ 29,017	$ 27,940
Concentration Risk,Percentage	100.00%	100.00%
Loans receivable at fair value	$ 7,834	$ 7,824
Commercial real estate [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans and Leases Receivable, Gross	$ 16,830	$ 17,743
Concentration Risk,Percentage	100.00%	100.00%
Loans receivable at fair value	$ 2,005	$ 1,876
Residential real estate [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans and Leases Receivable, Gross	$ 4,413	$ 6,958
Concentration Risk,Percentage	100.00%	100.00%
Loans receivable at fair value	$ 474	$ 792
Installment [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans and Leases Receivable, Gross	$ 4,826	$ 4,747
Concentration Risk,Percentage	100.00%	100.00%
Credit Card Receivable [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans and Leases Receivable, Gross	$ 2,081	$ 1,858
Concentration Risk,Percentage	100.00%	100.00%
Other [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans and Leases Receivable, Gross	$ 5,624	$ 4,792
Concentration Risk,Percentage	100.00%	100.00%
Loans receivable at fair value	$ 601	$ 670
Internally rated loans [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans and Leases Receivable, Gross	$ 131,321	$ 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	$ 68,530	$ 46,307
Internally rated loans [Member] | Wealth management [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans and Leases Receivable, Gross	29,017	27,940
Internally rated loans [Member] | Commercial real estate [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans and Leases Receivable, Gross	16,830	17,743
Internally rated loans [Member] | Residential real estate [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans and Leases Receivable, Gross	4,413	6,958
Internally rated loans [Member] | Installment [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans and Leases Receivable, Gross	4,826	4,747
Internally rated loans [Member] | Credit Card Receivable [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans and Leases Receivable, Gross	2,081	1,858
Internally rated loans [Member] | Other [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans and Leases Receivable, Gross	$ 5,624	$ 4,792
Secured Loans [Member] | Internally rated loans [Member]
Financing Receivable, Recorded Investment [Line Items]
Concentration Risk,Percentage	78.00%	83.00%
Unsecured Loans [Member] | Internally rated loans [Member]
Financing Receivable, Recorded Investment [Line Items]
Concentration Risk,Percentage	22.00%	17.00%
Amortized cost [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans and Leases Receivable, Gross	$ 114,335	$ 90,636
Loans receivable at fair value	108,637	89,186
Amortized cost [Member] | Corporate [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans and Leases Receivable, Gross	63,697	41,129
Amortized cost [Member] | Wealth management [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans and Leases Receivable, Gross	21,183	20,116
Amortized cost [Member] | Commercial real estate [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans and Leases Receivable, Gross	14,165	13,258
Amortized cost [Member] | Residential real estate [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans and Leases Receivable, Gross	3,911	6,132
Amortized cost [Member] | Credit Card Receivable [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans and Leases Receivable, Gross	2,081	1,858
Amortized cost [Member] | Other [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans and Leases Receivable, Gross	4,472	3,396
Fair Value [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans receivable at fair value	13,829	14,386
Fair Value [Member] | Corporate [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans receivable at fair value	2,915	3,224
Fair Value [Member] | Wealth management [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans receivable at fair value	7,834	7,824
Fair Value [Member] | Commercial real estate [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans receivable at fair value	2,005	1,876
Fair Value [Member] | Residential real estate [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans receivable at fair value	474	792
Fair Value [Member] | Other [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans receivable at fair value	601	670
Fair Value [Member] | Internally rated loans [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans receivable at fair value	13,829	14,386
Held for sale [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans Receivable Held-for-sale, Amount	3,157	5,323
Loans receivable at fair value	3,210	5,409
Held for sale [Member] | Corporate [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans Receivable Held-for-sale, Amount	1,918	1,954
Held for sale [Member] | Commercial real estate [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans Receivable Held-for-sale, Amount	660	2,609
Held for sale [Member] | Residential real estate [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans Receivable Held-for-sale, Amount	28	34
Held for sale [Member] | Other [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans Receivable Held-for-sale, Amount	551	726
Held for sale [Member] | Internally rated loans [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans Receivable Held-for-sale, Amount	3,157	5,323
Loans Receivable [Member] | Amortized cost [Member] | Internally rated loans [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans and Leases Receivable, Gross	114,335	90,636
Loans Receivable [Member] | Investment-Grade [Member] | Internally rated loans [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans and Leases Receivable, Gross	$ 43,280	$ 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	$ 18,972	$ 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	20,393	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	478	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	259	244
Loans Receivable [Member] | Investment-Grade [Member] | Internally rated loans [Member] | Other [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans and Leases Receivable, Gross	$ 3,178	$ 2,375
Loans Receivable [Member] | Investment-Grade [Member] | Secured Loans [Member] | Internally rated loans [Member]
Financing Receivable, Recorded Investment [Line Items]
Concentration Risk,Percentage	67.00%	83.00%
Loans Receivable [Member] | Investment-Grade [Member] | Unsecured Loans [Member] | Internally rated loans [Member]
Financing Receivable, Recorded Investment [Line Items]
Concentration Risk,Percentage	33.00%	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	$ 40,637	$ 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	2,386	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	257	323
Loans Receivable [Member] | Non-Investment-Grade [Member] | Internally rated loans [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans and Leases Receivable, Gross	$ 71,081	$ 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	$ 49,050	$ 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	4,275	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	14,179	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	2,875	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	$ 702	$ 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	90.00%	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	10.00%	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	$ 64,397	$ 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	4,640	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	2,044	4,368
Loans Receivable [Member] | Unrated/Other [Member] | Internally rated loans [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans and Leases Receivable, Gross	$ 16,960	$ 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	$ 508	$ 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	4,349	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	2,173	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	1,279	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	4,826	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	2,081	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	$ 1,744	$ 1,335
Loans Receivable [Member] | Unrated/Other [Member] | Secured Loans [Member] | Internally rated loans [Member]
Financing Receivable, Recorded Investment [Line Items]
Concentration Risk,Percentage	54.00%	54.00%
Loans Receivable [Member] | Unrated/Other [Member] | Unsecured Loans [Member] | Internally rated loans [Member]
Financing Receivable, Recorded Investment [Line Items]
Concentration Risk,Percentage	46.00%	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	$ 9,301	$ 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	6,803	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	$ 856	$ 632