Amortized Cost to Fair Values of Securities Available for Sale (Detail) (USD $) In Millions, unless otherwise specified	Mar. 31, 2012	Dec. 31, 2011
Investment Holdings [Line Items]
Amortized Cost	$ 30,775.8	$ 30,092.6
Gross Unrealized Gains	188.8	173.8
Gross Unrealized Losses	57.8	73.9
Fair Value	30,906.8	30,192.5
U.S. Government
Investment Holdings [Line Items]
Amortized Cost	2,717.9	3,965.9
Gross Unrealized Gains	48.7	63.5
Gross Unrealized Losses	0.1
Fair Value	2,766.5	4,029.4
Obligations of States and Political Subdivisions
Investment Holdings [Line Items]
Amortized Cost	14.1	14.9
Gross Unrealized Gains	0.9	0.9
Fair Value	15.0	15.8
Government Sponsored Agency
Investment Holdings [Line Items]
Amortized Cost	17,521.6	16,702.6
Gross Unrealized Gains	96.6	86.1
Gross Unrealized Losses	12.9	17.3
Fair Value	17,605.3	16,771.4
Corporate Debt
Investment Holdings [Line Items]
Amortized Cost	2,831.2	2,677.7
Gross Unrealized Gains	9.8	4.7
Gross Unrealized Losses	1.3	5.7
Fair Value	2,839.7	2,676.7
Covered Bonds
Investment Holdings [Line Items]
Amortized Cost	1,355.9	746.1
Gross Unrealized Gains	22.5	9.2
Gross Unrealized Losses	2.0	0.4
Fair Value	1,376.4	754.9
Non-U.S. Government
Investment Holdings [Line Items]
Amortized Cost	192.2	173.7
Fair Value	192.2	173.7
Supranational Bonds
Investment Holdings [Line Items]
Amortized Cost	909.3	971.0
Gross Unrealized Gains	3.4	3.0
Gross Unrealized Losses	1.6	1.9
Fair Value	911.1	972.1
Residential Mortgage-Backed
Investment Holdings [Line Items]
Amortized Cost	161.4	196.1
Gross Unrealized Gains	0.1
Gross Unrealized Losses	23.9	32.3
Fair Value	137.6	163.8
Other Asset-Backed
Investment Holdings [Line Items]
Amortized Cost	2,035.8	1,606.8
Gross Unrealized Gains	1.9	1.3
Gross Unrealized Losses	2.7	3.3
Fair Value	2,035.0	1,604.8
Certificates of Deposit
Investment Holdings [Line Items]
Amortized Cost	2,448.4	2,418.2
Gross Unrealized Gains	0.8	0.2
Gross Unrealized Losses	0.7	0.3
Fair Value	2,448.5	2,418.1
Auction Rate Securities
Investment Holdings [Line Items]
Amortized Cost	184.7	186.5
Gross Unrealized Gains	3.9	4.3
Gross Unrealized Losses	12.3	12.5
Fair Value	176.3	178.3
Others
Investment Holdings [Line Items]
Amortized Cost	403.3	433.1
Gross Unrealized Gains	0.2	0.6
Gross Unrealized Losses	0.3	0.2
Fair Value	$ 403.2	$ 433.5

For an unclassified balance sheet, this item represents investments in debt and equity securities which are categorized neither as held-to-maturity nor trading.

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 320

-SubTopic 10

-Section 45

-Paragraph 1

-URI http://asc.fasb.org/extlink&oid=6871852&loc=d3e26610-111562

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

-Publisher FASB

-Name Statement of Financial Accounting Standard (FAS)

-Number 115

-Paragraph 12

-Subparagraph b

-LegacyDoc This reference is SUPERSEDED by the Accounting Standards Codification effective for interim and annual periods ending after September 15, 2009. This reference is included to help users transition from the previous accounting hierarchy and will be removed from future versions of this taxonomy.

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

-Publisher FASB

-Name FASB Staff Position (FSP)

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-LegacyDoc This reference is SUPERSEDED by the Accounting Standards Codification effective for interim and annual periods ending after September 15, 2009. This reference is included to help users transition from the previous accounting hierarchy and will be removed from future versions of this taxonomy.

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

-Publisher FASB

-Name Statement of Financial Accounting Standard (FAS)

-Number 133

-Paragraph 22

-LegacyDoc This reference is SUPERSEDED by the Accounting Standards Codification effective for interim and annual periods ending after September 15, 2009. This reference is included to help users transition from the previous accounting hierarchy and will be removed from future versions of this taxonomy.

Reference 5: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name FASB Staff Position (FSP)

-Number FAS115-1/124-1

-Paragraph 15D

-LegacyDoc This reference is SUPERSEDED by the Accounting Standards Codification effective for interim and annual periods ending after September 15, 2009. This reference is included to help users transition from the previous accounting hierarchy and will be removed from future versions of this taxonomy.

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

-Publisher FASB

-Name Statement of Financial Accounting Standard (FAS)

-Number 115

-Paragraph 13

-LegacyDoc This reference is SUPERSEDED by the Accounting Standards Codification effective for interim and annual periods ending after September 15, 2009. This reference is included to help users transition from the previous accounting hierarchy and will be removed from future versions of this taxonomy.

Reference 7: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

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-Number FAS115-1/124-1

-Paragraph 15C

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Reference 8: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Statement of Financial Accounting Standard (FAS)

-Number 115

-Paragraph 14

-LegacyDoc This reference is SUPERSEDED by the Accounting Standards Codification effective for interim and annual periods ending after September 15, 2009. This reference is included to help users transition from the previous accounting hierarchy and will be removed from future versions of this taxonomy.

Reference 9: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Statement of Financial Accounting Standard (FAS)

-Number 115

-Paragraph 16

-LegacyDoc This reference is SUPERSEDED by the Accounting Standards Codification effective for interim and annual periods ending after September 15, 2009. This reference is included to help users transition from the previous accounting hierarchy and will be removed from future versions of this taxonomy.

Reference 10: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 320

-SubTopic 10

-Section 25

-Paragraph 1

-Subparagraph (b)

-URI http://asc.fasb.org/extlink&oid=6379932&loc=d3e22054-111558

+ 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