Reconciliation of Amortized Cost to Fair Values of Securities Available for Sale (Detail) (USD $) In Millions, unless otherwise specified	Jun. 30, 2014	Dec. 31, 2013
Investment Holdings [Line Items]
Amortized Cost	$ 29,618.9	$ 28,382.3
Gross Unrealized Gains	129.0	174.2
Gross Unrealized Losses	58.5	163.7
Fair Value	29,689.4	28,392.8
U.S. Government
Investment Holdings [Line Items]
Amortized Cost	2,396.3	1,896.7
Gross Unrealized Gains	21.4	22.6
Gross Unrealized Losses		1.4
Fair Value	2,417.7	1,917.9
Obligations of States and Political Subdivisions
Investment Holdings [Line Items]
Amortized Cost	4.5	4.5
Gross Unrealized Gains	0.1	0.1
Fair Value	4.6	4.6
U.S. Government Sponsored Agency
Investment Holdings [Line Items]
Amortized Cost	18,112.8	17,495.2
Gross Unrealized Gains	79.7	80.7
Gross Unrealized Losses	23.6	47.9
Fair Value	18,168.9	17,528.0
Corporate Debt
Investment Holdings [Line Items]
Amortized Cost	3,696.3	3,615.2
Gross Unrealized Gains	5.6	10.5
Gross Unrealized Losses	31.2	101.2
Fair Value	3,670.7	3,524.5
Covered Bonds
Investment Holdings [Line Items]
Amortized Cost	1,974.6	1,898.9
Gross Unrealized Gains	14.3	50.9
Gross Unrealized Losses	0.1	5.9
Fair Value	1,988.8	1,943.9
Supranational, Sovereign and Non-U.S. Agency Bonds
Investment Holdings [Line Items]
Amortized Cost	720.6	717.0
Gross Unrealized Gains	2.6	5.3
Gross Unrealized Losses	0.9	1.7
Fair Value	722.3	720.6
Residential Mortgage-Backed
Investment Holdings [Line Items]
Amortized Cost	44.5	52.4
Gross Unrealized Gains	0.4	0.1
Gross Unrealized Losses	2.0	4.4
Fair Value	42.9	48.1
Other Asset-Backed
Investment Holdings [Line Items]
Amortized Cost	2,388.9	2,390.8
Gross Unrealized Gains	2.1	1.4
Gross Unrealized Losses		0.4
Fair Value	2,391.0	2,391.8
Auction Rate Securities
Investment Holdings [Line Items]
Amortized Cost	97.1	97.5
Gross Unrealized Gains	2.4	2.2
Gross Unrealized Losses	0.7	0.8
Fair Value	98.8	98.9
Others
Investment Holdings [Line Items]
Amortized Cost	183.3	214.1
Gross Unrealized Gains	0.4	0.4
Fair Value	$ 183.7	$ 214.5