Derivative Instruments - Effect of Fair Value and Cash Flow Hedge Accounting on Consolidated Statement of Income (Detail) - USD ($) $ in Millions	3 Months Ended
Mar. 31, 2018	Mar. 31, 2017
Other Noninterest Income [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Total amount of income line items presented in the Consolidated Statement of Income in which the effects of fair value or cash flow hedges are recorded	$ 167	$ 180
Other Noninterest Income [Member] \| Asset and Liability Management Positions [Member] \| Fair Value Hedges [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Amount of Gains (Losses) Recognized in Earnings related to fair value hedged item		10
Other Noninterest Income [Member] \| Asset and Liability Management Positions [Member] \| Fair Value Hedges [Member] \| Interest Rate Contracts [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Amount of Gains (Losses) Recognized in Earnings related to fair value hedge		(10)
Interest Expense [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Total amount of expense line items presented in the Consolidated Statement of Income in which the effects of fair value or cash flow hedges are recorded	623	413
Interest Expense [Member] \| Asset and Liability Management Positions [Member] \| Fair Value Hedges [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Amount of Gains (Losses) Recognized in Earnings related to fair value hedged item	43
Interest Expense [Member] \| Asset and Liability Management Positions [Member] \| Fair Value Hedges [Member] \| Interest Rate Contracts [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Amount of Gains (Losses) Recognized in Earnings related to fair value hedge	(43)
Interest Expense [Member] \| Asset and Liability Management Positions [Member] \| Cash Flow Hedges [Member] \| Interest Rate Contracts [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Amount of Gains (Losses) Recognized in Earnings related to cash flow hedge	$ 3	$ 14

Amount of gain (loss) from the increase (decrease) in fair value of derivative and nonderivative instruments designated as fair value hedging instruments recognized in the income statement.

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 815
-SubTopic 25
-Section 50
-Paragraph 1
-Subparagraph (a)(1)
-URI http://asc.fasb.org/extlink&oid=6886632&loc=d3e76258-113986

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Amount of the increase (decrease) in fair value of the hedged item in a fair value hedge recognized in the income statement.

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The amount of net gains or losses on interest rate cash flow hedges reclassified during the period to earnings from accumulated other comprehensive income upon the hedged transaction affecting earnings.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 815
-SubTopic 10
-Section 50
-Paragraph 4C
-Subparagraph (c)
-URI http://asc.fasb.org/extlink&oid=84234895&loc=SL5624171-113959

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Amount of expense line items presented in consolidated statement of income in which effects of fair value or cash flow hedges are recorded.

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Amount of income line items presented in consolidated statement of income in which effects of fair value or cash flow hedges are recorded.

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