Investment Securities - Summary of Remaining Contractual Principal Maturities for Available-for-Sale Securities (Detail) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020
Investments Classified By Contractual Maturity Date [Line Items]
Total	$ 27,221	$ 30,913
U.S. treasury securities
Investments Classified By Contractual Maturity Date [Line Items]
Total	15,850	4,470
U.S. agency debentures
Investments Classified By Contractual Maturity Date [Line Items]
Total	196	237
Foreign government debt securities
Investments Classified By Contractual Maturity Date [Line Items]
Total	61	24
Residential mortgage-backed securities | Agency-issued mortgage-backed securities
Investments Classified By Contractual Maturity Date [Line Items]
Total	8,589	13,503
Residential mortgage-backed securities | Agency-issued collateralized mortgage obligations - fixed rate
Investments Classified By Contractual Maturity Date [Line Items]
Total	982	8,107
Agency-issued commercial mortgage-backed securities
Investments Classified By Contractual Maturity Date [Line Items]
Total	1,543	$ 4,572
Available-for-sale Securities
Investments Classified By Contractual Maturity Date [Line Items]
Total	27,221
One Year or Less	388
After One Year to Five Years	15,194
After Five Years to Ten Years	2,068
After Ten Years	9,571
Available-for-sale Securities | U.S. treasury securities
Investments Classified By Contractual Maturity Date [Line Items]
Total	15,850
One Year or Less	247
After One Year to Five Years	15,091
After Five Years to Ten Years	512
After Ten Years	0
Available-for-sale Securities | U.S. agency debentures
Investments Classified By Contractual Maturity Date [Line Items]
Total	196
One Year or Less	80
After One Year to Five Years	36
After Five Years to Ten Years	80
After Ten Years	0
Available-for-sale Securities | Foreign government debt securities
Investments Classified By Contractual Maturity Date [Line Items]
Total	61
One Year or Less	61
After One Year to Five Years	0
After Five Years to Ten Years	0
After Ten Years	0
Available-for-sale Securities | Residential mortgage-backed securities | Agency-issued mortgage-backed securities
Investments Classified By Contractual Maturity Date [Line Items]
Total	8,589
One Year or Less	0
After One Year to Five Years	0
After Five Years to Ten Years	0
After Ten Years	8,589
Available-for-sale Securities | Residential mortgage-backed securities | Agency-issued collateralized mortgage obligations - fixed rate
Investments Classified By Contractual Maturity Date [Line Items]
Total	982
One Year or Less	0
After One Year to Five Years	0
After Five Years to Ten Years	0
After Ten Years	982
Available-for-sale Securities | Agency-issued commercial mortgage-backed securities
Investments Classified By Contractual Maturity Date [Line Items]
Total	1,543
One Year or Less	0
After One Year to Five Years	67
After Five Years to Ten Years	1,476
After Ten Years	$ 0
Lower Limit | Available-for-sale Securities
Investments Classified By Contractual Maturity Date [Line Items]
Mortgage-backed securities contractual maturities (in years)	10 years
Upper Limit | Available-for-sale Securities
Investments Classified By Contractual Maturity Date [Line Items]
Mortgage-backed securities contractual maturities (in years)	30 years