Reconciliation of Amortized Cost to Fair Values of Securities Available for Sale (Detail) (USD $) In Millions, unless otherwise specified	Mar. 31, 2013	Dec. 31, 2012
Investment Holdings [Line Items]
Amortized Cost	$ 26,959.0	$ 28,422.2
Gross Unrealized Gains	230.5	242.8
Gross Unrealized Losses	17.6	21.5
Fair Value	27,171.9	28,643.5
U.S. Government
Investment Holdings [Line Items]
Amortized Cost	1,748.1	1,747.9
Gross Unrealized Gains	34.3	36.7
Fair Value	1,782.4	1,784.6
Obligations of States and Political Subdivisions
Investment Holdings [Line Items]
Amortized Cost	13.9	13.9
Gross Unrealized Gains	0.8	0.2
Fair Value	14.7	14.1
U.S. Government Sponsored Agency
Investment Holdings [Line Items]
Amortized Cost	16,747.3	18,520.6
Gross Unrealized Gains	116.7	122.2
Gross Unrealized Losses	4.6	4.0
Fair Value	16,859.4	18,638.8
Corporate Debt
Investment Holdings [Line Items]
Amortized Cost	2,927.7	2,602.4
Gross Unrealized Gains	17.4	18.1
Gross Unrealized Losses	3.3	2.1
Fair Value	2,941.8	2,618.4
Covered Bonds
Investment Holdings [Line Items]
Amortized Cost	1,820.6	1,697.1
Gross Unrealized Gains	47.9	51.0
Gross Unrealized Losses		0.1
Fair Value	1,868.5	1,748.0
Supranational and Non-U.S. Agency Bonds
Investment Holdings [Line Items]
Amortized Cost	808.7
Gross Unrealized Gains	7.0
Fair Value	815.7
Residential Mortgage-Backed
Investment Holdings [Line Items]
Amortized Cost	78.7	102.4
Gross Unrealized Gains	0.1	0.4
Gross Unrealized Losses	7.9	10.8
Fair Value	70.9	92.0
Other Asset-Backed
Investment Holdings [Line Items]
Amortized Cost	2,436.0	2,280.0
Gross Unrealized Gains	3.1	4.3
Gross Unrealized Losses	0.4	0.4
Fair Value	2,438.7	2,283.9
Auction Rate Securities
Investment Holdings [Line Items]
Amortized Cost	98.7	99.6
Gross Unrealized Gains	2.3	2.1
Gross Unrealized Losses	1.4	3.9
Fair Value	99.6	97.8
Others
Investment Holdings [Line Items]
Amortized Cost	279.3	304.4
Gross Unrealized Gains	0.9	0.8
Fair Value	280.2	305.2
Supranational Bonds
Investment Holdings [Line Items]
Amortized Cost		1,053.9
Gross Unrealized Gains		7.0
Gross Unrealized Losses		0.2
Fair Value		$ 1,060.7

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

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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