Reconciliation of the Beginning and Ending Balances for Fair Valued Assets and Liabilities Measured on a Recurring Basis Using Significant Unobservable Inputs (Detail) - USD ($) $ in Millions	3 Months Ended				9 Months Ended
	Sep. 30, 2019		Sep. 30, 2018		Sep. 30, 2019		Sep. 30, 2018		Jun. 30, 2019	Dec. 31, 2018	Jun. 30, 2018	Dec. 31, 2017
Derivative contracts, net [Member]
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset Value	$ 17		$ 3		$ 17		$ 3		$ 24	$ 13	$ 3	$ 0
Included in earnings	60	[1]	18	[2]	147	[1]	36	[2]
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset, Gain (Loss) Included in Other Comprehensive Income (Loss)	0		0		0		0
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset, Purchases	0		0		0		0
Sales	0		0		0		0
Settlements	(3)		(8)		(5)		(10)
Transfers to other balance sheet line items	(64)	[3]	(26)	[4]	(138)	[3]	(43)	[4]
Transfers into Level 3	0		0		0		0
Transferred Out of Level 3 in The Fair Value Hierarchy	0		0		0		0
Fair Value, Asset, Recurring Basis, Still Held, Unrealized Gain (Loss)	23		10		23		7
Mortgage-backed Securities, Issued by Private Enterprises [Member]
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset Value			0				0					59
Included in earnings							0
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset, Gain (Loss) Included in Other Comprehensive Income (Loss)							0
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset, Purchases							0
Sales							0
Settlements							(2)
Transfers to other balance sheet line items							0
Transfers into Level 3							0
Transferred Out of Level 3 in The Fair Value Hierarchy							(57)
Asset-backed Securities [Member]
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset Value			0				0					8
Included in earnings							0
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset, Gain (Loss) Included in Other Comprehensive Income (Loss)							0
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset, Purchases							0
Sales							0
Settlements							(1)
Transfers to other balance sheet line items							0
Transfers into Level 3							0
Transferred Out of Level 3 in The Fair Value Hierarchy							(7)
Corporate Debt Securities [Member]
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset Value			0				0					5
Included in earnings							0
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset, Gain (Loss) Included in Other Comprehensive Income (Loss)							0
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset, Purchases							0
Sales							0
Settlements							0
Transfers to other balance sheet line items							0
Transfers into Level 3							0
Transferred Out of Level 3 in The Fair Value Hierarchy							(5)
Available-for-sale Securities [Member]
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset Value			0				0					72
Included in earnings							0
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset, Gain (Loss) Included in Other Comprehensive Income (Loss)							0
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset, Purchases							0
Sales							0
Settlements							(3)
Transfers to other balance sheet line items							0
Transfers into Level 3							0
Transferred Out of Level 3 in The Fair Value Hierarchy							(69)
Loans Held-For-Investment [Member]
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset Value	124		168		124		168		$ 127	$ 163	$ 177	$ 196
Included in earnings	2	[5]	0	[6]	5	[5]	(3)	[6]
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset, Gain (Loss) Included in Other Comprehensive Income (Loss)	0		0		0		0
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset, Purchases	0		0		0		0
Sales	0		0		0		0
Settlements	(6)		(9)		(21)		(26)
Transfers to other balance sheet line items	0		0		0		0
Transfers into Level 3	1		0		2		1
Transferred Out of Level 3 in The Fair Value Hierarchy	0		0		(25)		0
Fair Value, Asset, Recurring Basis, Still Held, Unrealized Gain (Loss)	3		0		5		(4)
Interest Rate Lock Commitments [Member]
Transferred Out of Level 3 in The Fair Value Hierarchy	$ (64)		$ 26		$ (138)		$ 43

[1] Includes issuances, fair value changes, and expirations. Amount related to residential IRLCs is recognized in Mortgage-related income, amount related to commercial IRLCs is recognized in Commercial real estate-related income, and amount related to Visa derivative liability is recognized in Other noninterest expense. Included $23 million in earnings during both the three and nine months ended September 30, 2019, related to changes in unrealized gains on net derivative instruments still held at September 30, 2019.

[2] Includes issuances, fair value changes, and expirations. Amount related to residential IRLCs is recognized in Mortgage-related income, amount related to commercial IRLCs is recognized in Commercial real estate-related income, and amount related to Visa derivative liability is recognized in Other noninterest expense. Included $10 million and $7 million in earnings during the three and nine months ended September 30, 2018, respectively, related to changes in unrealized gains on net derivative instruments still held at September 30, 2018.

[3] During the three and nine months ended September 30, 2019, the Company transferred $64 million and $138 million, respectively, of net IRLC assets out of level 3 as the associated loans were closed.

[4] During the three and nine months ended September 30, 2018, the Company transferred $26 million and $43 million, respectively, of net IRLC assets out of level 3 as the associated loans were closed.

[5] Amounts are generally included in Mortgage-related income; however, the mark on certain fair value loans is included in Other noninterest income. Included $3 million and $5 million in earnings during the three and nine months ended September 30, 2019, respectively, related to changes in unrealized gains on LHFI still held at September 30, 2019.

[6] Amounts are generally included in Mortgage-related income; however, the mark on certain fair value loans is included in Other noninterest income. Included $0 and $4 million in earnings during the three and nine months ended September 30, 2018, respectively, related to changes in unrealized losses on LHFI still held at September 30, 2018.