Loans Held for Investment portfolio and Related Allowance for Loan and Lease Losses (Detail) - USD ($) $ in Millions		Sep. 30, 2018	Jun. 30, 2018	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Dec. 31, 2016
Individually evaluated		$ 2,747		$ 2,821
Financing Receivable, Allowance for Credit Losses, Individually Evaluated for Impairment		192		204
Collectively evaluated		144,300		140,164
Financing Receivable, Allowance for Credit Losses, Collectively Evaluated for Impairment		1,431		1,531
Total evaluated		147,047		142,985
Loans And Leases Receivable Allowance Loans Evaluated For Impairment Excluding Fair Value Loans		1,623		1,735
Loans Receivable, Fair Value Disclosure		168		196
Total	[1]	147,215		143,181
Loans and Leases Receivable, Allowance		1,623	$ 1,650	1,735	$ 1,772	$ 1,731	$ 1,709
Commercial Portfolio Segment [Member]
Individually evaluated		238		173
Financing Receivable, Allowance for Credit Losses, Individually Evaluated for Impairment		28		21
Collectively evaluated		77,720		75,304
Financing Receivable, Allowance for Credit Losses, Collectively Evaluated for Impairment		1,034		1,080
Total evaluated		77,958		75,477
Loans And Leases Receivable Allowance Loans Evaluated For Impairment Excluding Fair Value Loans		1,062		1,101
Loans Receivable, Fair Value Disclosure		0		0
Total		77,958		75,477
Loans and Leases Receivable, Allowance		1,062	1,068	1,101	1,123	1,140	1,124
Residential Portfolio Segment [Member]
Total		38,505		38,620
Consumer Portfolio Segment [Member]
Individually evaluated		2,509		2,648
Financing Receivable, Allowance for Credit Losses, Individually Evaluated for Impairment		164		183
Collectively evaluated		66,580		64,860
Financing Receivable, Allowance for Credit Losses, Collectively Evaluated for Impairment		397		451
Total evaluated		69,089		67,508
Loans And Leases Receivable Allowance Loans Evaluated For Impairment Excluding Fair Value Loans		561		634
Loans Receivable, Fair Value Disclosure		168		196
Total		69,257		67,704
Loans and Leases Receivable, Allowance		$ 561	$ 582	$ 634	$ 649	$ 591	$ 585

[1] Includes loans of consolidated VIEs of $159 million and $179 million at September 30, 2018 and December 31, 2017, respectively.