Investment Securities - Gross Unrealized Losses and Fair Value of Company's Investment Securities (Detail) $ in Millions	Jun. 30, 2020 USD ($)
Continuous Gross Unrealized Losses And Fair Value [Abstract]
Fair Value Less Than 12 Months	$ 3,050
Unrealized Losses Less Than 12 Months	(19)
Fair Value 12 Months or Greater	4,987
Unrealized Losses 12 Months or Greater	(20)
Fair Value Total	8,037
Unrealized Losses Total	(39)
Other Asset-Backed Securities [Member]
Continuous Gross Unrealized Losses And Fair Value [Abstract]
Fair Value 12 Months or Greater	2
Fair Value Total	2
U.S. Treasury and Agencies [Member]
Continuous Gross Unrealized Losses And Fair Value [Abstract]
Fair Value Less Than 12 Months	143
Fair Value Total	143
Residential Mortgage-Backed Securities [Member]
Continuous Gross Unrealized Losses And Fair Value [Abstract]
Fair Value Less Than 12 Months	2,821
Unrealized Losses Less Than 12 Months	(18)
Fair Value 12 Months or Greater	4,985
Unrealized Losses 12 Months or Greater	(20)
Fair Value Total	7,806
Unrealized Losses Total	(38)
Obligations of State and Political Subdivisions [Member]
Continuous Gross Unrealized Losses And Fair Value [Abstract]
Fair Value Less Than 12 Months	80
Unrealized Losses Less Than 12 Months	(1)
Fair Value Total	80
Unrealized Losses Total	(1)
Obligations of Foreign Governments [Member]
Continuous Gross Unrealized Losses And Fair Value [Abstract]
Fair Value Less Than 12 Months	2
Fair Value Total	2
Corporate Debt Securities [Member]
Continuous Gross Unrealized Losses And Fair Value [Abstract]
Fair Value Less Than 12 Months	4
Fair Value Total	$ 4

Amount of investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale), in continuous unrealized loss position for more than 12 months, without allowance for credit loss. Includes beneficial interest in securitized financial asset.

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