Accumulated Other Comprehensive Income (Loss) Changes During Period (Detail) (USD $) In Millions, unless otherwise specified	3 Months Ended
	Mar. 31, 2012	Mar. 31, 2011
Accumulated Other Comprehensive Income (Loss) [Line Items]
Other Comprehensive Income, After Tax	$ 69.3	$ 25.7
Net Unrealized Gains (Losses) on Securities Available for Sale
Accumulated Other Comprehensive Income (Loss) [Line Items]
Before Tax	32.0	5.3
Tax Effect	(12.0)	(1.9)
Other Comprehensive Income, After Tax	20.0	3.4
Net Unrealized Gains (Losses) on Securities Available for Sale | Noncredit-Related Unrealized Losses on Securities OTTI
Accumulated Other Comprehensive Income (Loss) [Line Items]
Before Tax	5.8	5.1
Tax Effect	(2.2)	(1.9)
Other Comprehensive Income, After Tax	3.6	3.2
Net Unrealized Gains (Losses) on Securities Available for Sale | Other Unrealized Gains (Losses) on Securities Available-for-Sale
Accumulated Other Comprehensive Income (Loss) [Line Items]
Before Tax	29.6	(0.3)
Tax Effect	(11.1)	0.2
Other Comprehensive Income, After Tax	18.5	(0.1)
Net Unrealized Gains (Losses) on Securities Available for Sale | Reclassification Adjustments
Accumulated Other Comprehensive Income (Loss) [Line Items]
Before Tax	(3.4)	0.5
Tax Effect	1.3	(0.2)
Other Comprehensive Income, After Tax	(2.1)	0.3
Net Unrealized Gains (Losses) on Cash Flow Hedge Designations
Accumulated Other Comprehensive Income (Loss) [Line Items]
Before Tax	17.9	14.3
Tax Effect	(6.6)	(5.3)
Other Comprehensive Income, After Tax	11.3	9.0
Net Unrealized Gains (Losses) on Cash Flow Hedge Designations | Unrealized Gains (Losses) on Cash Flow Hedge Designations
Accumulated Other Comprehensive Income (Loss) [Line Items]
Before Tax	18.9	16.8
Tax Effect	(7.0)	(6.2)
Other Comprehensive Income, After Tax	11.9	10.6
Net Unrealized Gains (Losses) on Cash Flow Hedge Designations | Reclassification Adjustment
Accumulated Other Comprehensive Income (Loss) [Line Items]
Before Tax	(1.0)	(2.5)
Tax Effect	0.4	0.9
Other Comprehensive Income, After Tax	(0.6)	(1.6)
Foreign Currency Translation Adjustments
Accumulated Other Comprehensive Income (Loss) [Line Items]
Before Tax	(10.3)	(6.9)
Tax Effect	26.1	14.1
Other Comprehensive Income, After Tax	15.8	7.2
Foreign Currency Translation Adjustments | Foreign Currency Translation Adjustment Gain (Loss)
Accumulated Other Comprehensive Income (Loss) [Line Items]
Before Tax	34.9	59.9
Other Comprehensive Income, After Tax	34.9	59.9
Foreign Currency Translation Adjustments | Net Investment Hedge Gains (Losses)
Accumulated Other Comprehensive Income (Loss) [Line Items]
Before Tax	(45.2)	(66.8)
Tax Effect	26.1	14.1
Other Comprehensive Income, After Tax	(19.1)	(52.7)
Net Pension and Other Postretirement Benefit Adjustments
Accumulated Other Comprehensive Income (Loss) [Line Items]
Before Tax	35.4	7.5
Tax Effect	(13.2)	(1.4)
Other Comprehensive Income, After Tax	22.2	6.1
Net Pension and Other Postretirement Benefit Adjustments | Net Actuarial (Loss) Gain
Accumulated Other Comprehensive Income (Loss) [Line Items]
Before Tax	26.7
Tax Effect	(10.1)
Other Comprehensive Income, After Tax	16.6
Net Pension and Other Postretirement Benefit Adjustments | Pension and Other Postretirement Benefit Adjustments
Accumulated Other Comprehensive Income (Loss) [Line Items]
Before Tax	8.7	7.5
Tax Effect	(3.1)	(1.4)
Other Comprehensive Income, After Tax	$ 5.6	$ 6.1