Accumulated Other Comprehensive Income (Loss) Changes During Period (Detail) (USD $) In Millions, unless otherwise specified	3 Months Ended		9 Months Ended
	Sep. 30, 2012	Sep. 30, 2011	Sep. 30, 2012	Sep. 30, 2011
Accumulated Other Comprehensive Income (Loss) [Line Items]
Other Comprehensive Income	$ 58.2	$ 10.8	$ 129.7	$ 72.8
Net Unrealized Gains (Losses) on Securities Available for Sale
Accumulated Other Comprehensive Income (Loss) [Line Items]
Before Tax	57.1	34.4	107.7	88.1
Tax Effect	(21.5)	(13.0)	(40.4)	(32.9)
Other Comprehensive Income	35.6	21.4	67.3	55.2
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	4.9	(0.4)	15.0	11.5
Tax Effect	(1.8)	0.1	(5.6)	(4.2)
Other Comprehensive Income	3.1	(0.3)	9.4	7.3
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	57.3	32.5	105.9	64.2
Tax Effect	(21.6)	(12.3)	(39.7)	(24.1)
Other Comprehensive Income	35.7	20.2	66.2	40.1
Net Unrealized Gains (Losses) on Securities Available for Sale | Reclassification Adjustment for (Gains) Losses Included in Net Income
Accumulated Other Comprehensive Income (Loss) [Line Items]
Before Tax	(5.1)	2.3	(13.2)	12.4
Tax Effect	1.9	(0.8)	4.9	(4.6)
Other Comprehensive Income	(3.2)	1.5	(8.3)	7.8
Net Unrealized Gains (Losses) on Cash Flow Hedge Designations
Accumulated Other Comprehensive Income (Loss) [Line Items]
Before Tax	4.6	(26.5)	8.4	(15.3)
Tax Effect	(1.5)	9.9	(2.9)	5.7
Other Comprehensive Income	3.1	(16.6)	5.5	(9.6)
Net Unrealized Gains (Losses) on Cash Flow Hedge Designations | Reclassification Adjustment for (Gains) Losses Included in Net Income
Accumulated Other Comprehensive Income (Loss) [Line Items]
Before Tax	2.6	(1.9)	3.7	(6.5)
Tax Effect	(1.0)	0.7	(1.4)	2.4
Other Comprehensive Income	1.6	(1.2)	2.3	(4.1)
Net Unrealized Gains (Losses) on Cash Flow Hedge Designations | Unrealized Gains (Losses) on Cash Flow Hedges
Accumulated Other Comprehensive Income (Loss) [Line Items]
Before Tax	2.0	(24.6)	4.7	(8.8)
Tax Effect	(0.5)	9.2	(1.5)	3.3
Other Comprehensive Income	1.5	(15.4)	3.2	(5.5)
Foreign Currency Translation Adjustments
Accumulated Other Comprehensive Income (Loss) [Line Items]
Before Tax	(2.7)	31.2	13.9	19.7
Tax Effect	16.9	(30.0)	10.2	(9.1)
Other Comprehensive Income	14.2	1.2	24.1	10.6
Foreign Currency Translation Adjustments | Foreign Currency Translation Adjustments
Accumulated Other Comprehensive Income (Loss) [Line Items]
Before Tax	42.1	(50.1)	31.3	23.8
Other Comprehensive Income	42.1	(50.1)	31.3	23.8
Foreign Currency Translation Adjustments | Net Investment Hedge Gains (Losses)
Accumulated Other Comprehensive Income (Loss) [Line Items]
Before Tax	(44.8)	81.3	(17.4)	(4.1)
Tax Effect	16.9	(30.0)	10.2	(9.1)
Other Comprehensive Income	(27.9)	51.3	(7.2)	(13.2)
Net Pension and Other Postretirement Benefit Adjustments
Accumulated Other Comprehensive Income (Loss) [Line Items]
Before Tax	8.5	7.6	52.3	22.3
Tax Effect	(3.2)	(2.8)	(19.5)	(5.7)
Other Comprehensive Income	5.3	4.8	32.8	16.6
Net Pension and Other Postretirement Benefit Adjustments | Net Actuarial Gain (Loss)
Accumulated Other Comprehensive Income (Loss) [Line Items]
Before Tax			26.7	(0.3)
Tax Effect			(10.1)	0.1
Other Comprehensive Income			16.6	(0.2)
Net Pension and Other Postretirement Benefit Adjustments | Reclassification Adjustment for (Gains) Losses Included in Net Income
Accumulated Other Comprehensive Income (Loss) [Line Items]
Before Tax	8.5	7.6	25.6	22.6
Tax Effect	(3.2)	(2.8)	(9.4)	(5.8)
Other Comprehensive Income	$ 5.3	$ 4.8	$ 16.2	$ 16.8