Liability for Unpaid Claims Recon (Detail) (USD $) In Millions, unless otherwise specified	12 Months Ended
	Dec. 31, 2011	Dec. 31, 2010	Dec. 31, 2009
Causes of Increase (Decrease) in Liability for Unpaid Claims and Claims Adjustment Expense [Line Items]
Balance at January 1	$ 24,339.4	$ 24,585.7	$ 24,419.0
Less Reinsurance Recoverable	2,028.2	2,179.3	2,226.3
Net Balance at January 1	22,311.2	22,406.4	22,192.7
Incurred Related to
Current Year	4,684.4	4,517.9	4,433.3
Total Incurred	6,145.5	5,651.6	5,890.7
Paid Related to
Current Year	(1,588.6)	(1,514.8)	(1,451.6)
Prior Years	(4,324.2)	(4,232.0)	(4,225.4)
Total Paid	(5,912.8)	(5,746.8)	(5,677.0)
Net Balance at December 31	22,543.9	22,311.2	22,406.4
Plus Reinsurance Recoverable	2,042.6	2,028.2	2,179.3
Balance at December 31	24,586.5	24,339.4	24,585.7
Interest Expense [Member]
Incurred Related to
Prior Years	1,262.9	1,268.9	1,285.4
Other Noninterest Expense [Member]
Incurred Related to
Prior Years	209.1	(61.3)	(34.7)
Foreign Currency Gain (Loss) [Member]
Incurred Related to
Prior Years	$ (10.9)	$ (73.9)	$ 206.7