Amortized Cost to Fair Values of Securities Available for Sale (Detail) (USD $) In Millions, unless otherwise specified	Sep. 30, 2012	Dec. 31, 2011
Investment Holdings [Line Items]
Amortized Cost	$ 27,896.8	$ 30,092.6
Gross Unrealized Gains	262.5	173.8
Gross Unrealized Losses	23.2	73.9
Fair Value	28,136.1	30,192.5
U.S. Government
Investment Holdings [Line Items]
Amortized Cost	1,747.7	3,965.9
Gross Unrealized Gains	40.1	63.5
Fair Value	1,787.8	4,029.4
Obligations of States and Political Subdivisions
Investment Holdings [Line Items]
Amortized Cost	14.1	14.9
Gross Unrealized Gains	0.2	0.9
Fair Value	14.3	15.8
Government Sponsored Agency
Investment Holdings [Line Items]
Amortized Cost	18,456.4	16,702.6
Gross Unrealized Gains	132.7	86.1
Gross Unrealized Losses	4.0	17.3
Fair Value	18,585.1	16,771.4
Corporate Debt
Investment Holdings [Line Items]
Amortized Cost	2,155.7	2,677.7
Gross Unrealized Gains	18.3	4.7
Gross Unrealized Losses	0.4	5.7
Fair Value	2,173.6	2,676.7
Covered Bonds
Investment Holdings [Line Items]
Amortized Cost	1,678.0	746.1
Gross Unrealized Gains	55.8	9.2
Gross Unrealized Losses		0.4
Fair Value	1,733.8	754.9
Non-U.S. Government
Investment Holdings [Line Items]
Amortized Cost		173.7
Fair Value		173.7
Supranational Bonds
Investment Holdings [Line Items]
Amortized Cost	1,040.1	971.0
Gross Unrealized Gains	7.0	3.0
Gross Unrealized Losses	0.5	1.9
Fair Value	1,046.6	972.1
Residential Mortgage-Backed
Investment Holdings [Line Items]
Amortized Cost	127.5	196.1
Gross Unrealized Gains	1.6
Gross Unrealized Losses	13.3	32.3
Fair Value	115.8	163.8
Other Asset-Backed
Investment Holdings [Line Items]
Amortized Cost	2,235.5	1,606.8
Gross Unrealized Gains	4.8	1.3
Gross Unrealized Losses	0.7	3.3
Fair Value	2,239.6	1,604.8
Certificates of Deposit
Investment Holdings [Line Items]
Amortized Cost		2,418.2
Gross Unrealized Gains		0.2
Gross Unrealized Losses		0.3
Fair Value		2,418.1
Auction Rate Securities
Investment Holdings [Line Items]
Amortized Cost	102.8	186.5
Gross Unrealized Gains	1.0	4.3
Gross Unrealized Losses	4.3	12.5
Fair Value	99.5	178.3
Others
Investment Holdings [Line Items]
Amortized Cost	339.0	433.1
Gross Unrealized Gains	1.0	0.6
Gross Unrealized Losses		0.2
Fair Value	$ 340.0	$ 433.5

Amount of investment in debt and equity securities categorized neither as held-to-maturity nor trading.

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-Publisher FASB

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-Number FAS115-1/124-1

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Reference 2: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Statement of Financial Accounting Standard (FAS)

-Number 115

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Reference 3: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 320

-SubTopic 10

-Section 45

-Paragraph 1

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Reference 4: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

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Reference 6: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 320

-SubTopic 10

-Section 25

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-Number 115

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+ Details

- Definition

This item represents the cost of debt and equity securities, which are categorized neither as held-to-maturity nor trading, net of adjustments including accretion, amortization, collection of cash, previous other-than-temporary impairments recognized in earnings (less any cumulative-effect adjustments recognized, as defined), and fair value hedge accounting adjustments, if any.

+ References+ Details

- Definition

This item represents the gross unrealized gains for securities, at a point in time, which are categorized neither as held-to-maturity nor trading securities.

+ References+ Details