Loans - Summary of Weighted Average of Significant Unobservable Inputs (Detail) $ in Millions	Sep. 30, 2020 USD ($) yr	Dec. 31, 2019 USD ($) yr
Loans receivable at fair value | $	$ 13,881	$ 14,386
Level 3 [Member]
Loans receivable at fair value | $	2,827	1,890
Corporate [Member]
Loans receivable at fair value | $	2,856	3,224
Corporate [Member] | Level 3 [Member]
Loans receivable at fair value | $	1,003	752
Commercial real estate [Member]
Loans receivable at fair value | $	1,980	1,876
Commercial real estate [Member] | Level 3 [Member]
Loans receivable at fair value | $	1,166	591
Residential real estate [Member]
Loans receivable at fair value | $	446	792
Residential real estate [Member] | Level 3 [Member]
Loans receivable at fair value | $	269	221
Wealth management and other [Member] | Level 3 [Member]
Loans receivable at fair value | $	$ 389	$ 326
Minimum [Member] | Fair Value Unobservable Inputs, Yield [Member] | Corporate [Member] | Level 3 [Member]
Loans Receivable, Measurement Input	0.021	0.019
Minimum [Member] | Fair Value Unobservable Inputs, Yield [Member] | Commercial real estate [Member] | Level 3 [Member]
Loans Receivable, Measurement Input	0.045	0.070
Minimum [Member] | Fair Value Unobservable Inputs, Yield [Member] | Residential real estate [Member] | Level 3 [Member]
Loans Receivable, Measurement Input	0.015	0.011
Minimum [Member] | Fair Value Unobservable Inputs, Yield [Member] | Wealth management and other [Member] | Level 3 [Member]
Loans Receivable, Measurement Input	0.090	0.039
Minimum [Member] | Fair Value Unobservable Inputs, Recovery Rate [Member] | Corporate [Member] | Level 3 [Member]
Loans Receivable, Measurement Input	0.150	0.135
Minimum [Member] | Fair Value Unobservable Inputs, Recovery Rate [Member] | Commercial real estate [Member] | Level 3 [Member]
Loans Receivable, Measurement Input	0.033	0.059
Minimum [Member] | Fair Value Unobservable Inputs, Duration [Member] | Corporate [Member] | Level 3 [Member]
Loans Receivable, Measurement Input	3.0	3.7
Minimum [Member] | Fair Value Unobservable Inputs, Duration [Member] | Commercial real estate [Member] | Level 3 [Member]
Loans Receivable, Measurement Input	0.1	0.2
Minimum [Member] | Fair Value Unobservable Inputs, Duration [Member] | Residential real estate [Member] | Level 3 [Member]
Loans Receivable, Measurement Input	0.7	1.1
Minimum [Member] | Fair Value Unobservable Inputs, Duration [Member] | Wealth management and other [Member] | Level 3 [Member]
Loans Receivable, Measurement Input	1.0	1.6
Maximum [Member] | Fair Value Unobservable Inputs, Yield [Member] | Corporate [Member] | Level 3 [Member]
Loans Receivable, Measurement Input	0.244	0.263
Maximum [Member] | Fair Value Unobservable Inputs, Yield [Member] | Commercial real estate [Member] | Level 3 [Member]
Loans Receivable, Measurement Input	0.263	0.160
Maximum [Member] | Fair Value Unobservable Inputs, Yield [Member] | Residential real estate [Member] | Level 3 [Member]
Loans Receivable, Measurement Input	0.140	0.140
Maximum [Member] | Fair Value Unobservable Inputs, Yield [Member] | Wealth management and other [Member] | Level 3 [Member]
Loans Receivable, Measurement Input	0.187	0.160
Maximum [Member] | Fair Value Unobservable Inputs, Recovery Rate [Member] | Corporate [Member] | Level 3 [Member]
Loans Receivable, Measurement Input	0.700	0.780
Maximum [Member] | Fair Value Unobservable Inputs, Recovery Rate [Member] | Commercial real estate [Member] | Level 3 [Member]
Loans Receivable, Measurement Input	0.983	0.852
Maximum [Member] | Fair Value Unobservable Inputs, Duration [Member] | Corporate [Member] | Level 3 [Member]
Loans Receivable, Measurement Input	5.5	5.8
Maximum [Member] | Fair Value Unobservable Inputs, Duration [Member] | Commercial real estate [Member] | Level 3 [Member]
Loans Receivable, Measurement Input	4.3	5.3
Maximum [Member] | Fair Value Unobservable Inputs, Duration [Member] | Residential real estate [Member] | Level 3 [Member]
Loans Receivable, Measurement Input	3.1	4.8
Maximum [Member] | Fair Value Unobservable Inputs, Duration [Member] | Wealth management and other [Member] | Level 3 [Member]
Loans Receivable, Measurement Input	5.2	6.7
Weighted Average [Member] | Fair Value Unobservable Inputs, Yield [Member] | Corporate [Member] | Level 3 [Member]
Loans Receivable, Measurement Input	0.089	0.095
Weighted Average [Member] | Fair Value Unobservable Inputs, Yield [Member] | Commercial real estate [Member] | Level 3 [Member]
Loans Receivable, Measurement Input	0.111	0.093
Weighted Average [Member] | Fair Value Unobservable Inputs, Yield [Member] | Residential real estate [Member] | Level 3 [Member]
Loans Receivable, Measurement Input	0.119	0.115
Weighted Average [Member] | Fair Value Unobservable Inputs, Yield [Member] | Wealth management and other [Member] | Level 3 [Member]
Loans Receivable, Measurement Input	0.097	0.099
Weighted Average [Member] | Fair Value Unobservable Inputs, Recovery Rate [Member] | Corporate [Member] | Level 3 [Member]
Loans Receivable, Measurement Input	0.375	0.444
Weighted Average [Member] | Fair Value Unobservable Inputs, Recovery Rate [Member] | Commercial real estate [Member] | Level 3 [Member]
Loans Receivable, Measurement Input	0.690	0.486
Weighted Average [Member] | Fair Value Unobservable Inputs, Duration [Member] | Corporate [Member] | Level 3 [Member]
Loans Receivable, Measurement Input	4.2	3.9
Weighted Average [Member] | Fair Value Unobservable Inputs, Duration [Member] | Commercial real estate [Member] | Level 3 [Member]
Loans Receivable, Measurement Input	(2.8)	(3.5)
Weighted Average [Member] | Fair Value Unobservable Inputs, Duration [Member] | Residential real estate [Member] | Level 3 [Member]
Loans Receivable, Measurement Input	1.7	4.0
Weighted Average [Member] | Fair Value Unobservable Inputs, Duration [Member] | Wealth management and other [Member] | Level 3 [Member]
Loans Receivable, Measurement Input	3.0	3.7