Derivative Instruments - Impact of Derivative Instruments on Income Statement (Detail) - USD ($) $ in Millions	12 Months Ended
Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Fair Value Hedging \| Interest rate contracts \| Net interest revenue
Derivative Instruments, Gain (Loss) [Line Items]
Gain or (loss) recognized in income on derivatives Year ended Dec. 31,	$ (85.0)	$ (921.0)	$ 486.0
Gain or (loss) recognized in hedged item Year ended Dec. 31,	83.0	886.0	(468.0)
Cash flow hedges
Derivative Instruments, Gain (Loss) [Line Items]
Gain or (loss) recognized in accumulated OCI on derivatives(effective portion) Year ended Dec. 31,	0.0	22.0	131.0
Gain or (loss) reclassified from accumulated OCI into income (effective portion) Year ended Dec. 31,	(11.0)	41.0	124.0
Gain or (loss) recognized in income on derivatives (ineffectiveness portion and amount excluded from effectiveness testing) Year ended Dec. 31,	0.0	0.1	(0.1)
Cash flow hedges \| Foreign exchange contracts \| Net interest revenue
Derivative Instruments, Gain (Loss) [Line Items]
Gain or (loss) reclassified from accumulated OCI into income (effective portion) Year ended Dec. 31,	(1.0)	(2.0)	(28.0)
Gain or (loss) recognized in income on derivatives (ineffectiveness portion and amount excluded from effectiveness testing) Year ended Dec. 31,	0.0	0.0	0.0
Cash flow hedges \| Foreign exchange contracts \| Other revenue
Derivative Instruments, Gain (Loss) [Line Items]
Gain or (loss) reclassified from accumulated OCI into income (effective portion) Year ended Dec. 31,	0.0	(3.0)	(1.0)
Gain or (loss) recognized in income on derivatives (ineffectiveness portion and amount excluded from effectiveness testing) Year ended Dec. 31,	0.0	0.1	(0.1)
Cash flow hedges \| Foreign exchange contracts \| Trading revenue
Derivative Instruments, Gain (Loss) [Line Items]
Gain or (loss) reclassified from accumulated OCI into income (effective portion) Year ended Dec. 31,	9.0	36.0	154.0
Gain or (loss) recognized in income on derivatives (ineffectiveness portion and amount excluded from effectiveness testing) Year ended Dec. 31,	0.0	0.0	0.0
Cash flow hedges \| Foreign exchange contracts \| Salary expense
Derivative Instruments, Gain (Loss) [Line Items]
Gain or (loss) reclassified from accumulated OCI into income (effective portion) Year ended Dec. 31,	(19.0)	10.0	(1.0)
Gain or (loss) recognized in income on derivatives (ineffectiveness portion and amount excluded from effectiveness testing) Year ended Dec. 31,	0.0	0.0	0.0
Net Investment Hedging \| Foreign exchange contracts \| Net interest revenue
Derivative Instruments, Gain (Loss) [Line Items]
Gain or (loss) reclassified from accumulated OCI into income (effective portion) Year ended Dec. 31,	1.0	(1.0)	2.0
Net Investment Hedging \| Foreign exchange contracts \| Other revenue
Derivative Instruments, Gain (Loss) [Line Items]
Gain or (loss) recognized in income on derivatives (ineffectiveness portion and amount excluded from effectiveness testing) Year ended Dec. 31,	0.0	(0.1)	0.1
Accumulated Net Gain (Loss) from Cash Flow Hedges Including Portion Attributable to Noncontrolling Interest [Member] \| Cash flow hedges \| Foreign exchange contracts \| Net interest revenue
Derivative Instruments, Gain (Loss) [Line Items]
Gain or (loss) recognized in accumulated OCI on derivatives(effective portion) Year ended Dec. 31,	(1.0)	(2.0)	(27.0)
Accumulated Net Gain (Loss) from Cash Flow Hedges Including Portion Attributable to Noncontrolling Interest [Member] \| Cash flow hedges \| Foreign exchange contracts \| Other revenue
Derivative Instruments, Gain (Loss) [Line Items]
Gain or (loss) recognized in accumulated OCI on derivatives(effective portion) Year ended Dec. 31,	0.0	(6.0)	(3.0)
Accumulated Net Gain (Loss) from Cash Flow Hedges Including Portion Attributable to Noncontrolling Interest [Member] \| Cash flow hedges \| Foreign exchange contracts \| Trading revenue
Derivative Instruments, Gain (Loss) [Line Items]
Gain or (loss) recognized in accumulated OCI on derivatives(effective portion) Year ended Dec. 31,	9.0	36.0	154.0
Accumulated Net Gain (Loss) from Cash Flow Hedges Including Portion Attributable to Noncontrolling Interest [Member] \| Cash flow hedges \| Foreign exchange contracts \| Salary expense
Derivative Instruments, Gain (Loss) [Line Items]
Gain or (loss) recognized in accumulated OCI on derivatives(effective portion) Year ended Dec. 31,	(8.0)	(6.0)	7.0
Accumulated Net Gain (Loss) from Cash Flow Hedges Including Portion Attributable to Noncontrolling Interest [Member] \| Net Investment Hedging \| Foreign exchange contracts \| Net interest revenue
Derivative Instruments, Gain (Loss) [Line Items]
Gain or (loss) recognized in accumulated OCI on derivatives(effective portion) Year ended Dec. 31,	$ 474.0	$ (367.0)	$ (50.0)

Hedged Items, Gain (Loss) Recognized in Income, Net

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Amount of increase (decrease) in the fair value of derivatives recognized in the income statement.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 815
-SubTopic 10
-Section 50
-Paragraph 4A
-Subparagraph (b)
-URI http://asc.fasb.org/extlink&oid=56946850&loc=SL5618551-113959

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 815
-SubTopic 10
-Section 50
-Paragraph 4C
-Subparagraph (a),(c),(d),(e)
-URI http://asc.fasb.org/extlink&oid=56946850&loc=SL5624171-113959

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+ References

No definition available.

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The effective portion of net gain (loss) reclassified from accumulated other comprehensive income into income on derivative instruments designated and qualifying as hedging instruments.

+ 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=56946850&loc=SL5624171-113959

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 815
-SubTopic 10
-Section 50
-Paragraph 4D
-Subparagraph (b)
-URI http://asc.fasb.org/extlink&oid=56946850&loc=SL5624177-113959

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The portion of gains and losses (net) on derivative instruments designated and qualifying as hedging instruments representing (a) the amount of the hedge ineffectiveness and (b) the amount, if any, excluded from the assessment of hedge effectiveness.

+ 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 (d)
-URI http://asc.fasb.org/extlink&oid=56946850&loc=SL5624171-113959

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 815
-SubTopic 25
-Section 50
-Paragraph 1
-Subparagraph (a)(1),(2)
-URI http://asc.fasb.org/extlink&oid=6886632&loc=d3e76258-113986

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The effective portion of gains and losses (net) on derivative instruments designated and qualifying as hedging instruments that was recognized in other comprehensive income during the current period.

+ References

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