Parent Company Balance Sheet (Detail) (USD $) In Millions, unless otherwise specified	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011
Assets [Abstract]
Fixed Maturity Securities	$ 42,344.4	$ 44,973.0
Other Long-term Investments	566.0	625.0
Short-term Investments	913.4	1,460.3
Other Assets	647.8	625.4
Total Assets	59,403.6	62,236.1
Liabilities
Short-term Debt	76.5	455.8
Long-term Debt	2,612.0	2,755.4
Other Liabilities	1,229.4	1,838.1
Total Liabilities	50,744.5	53,623.5
Stockholders' Equity
Common Stock	36.1	36.0
Additional Paid-in Capital	2,634.1	2,607.7
Accumulated Other Comprehensive Income	255.0	628.0
Retained Earnings	8,083.2	7,371.6
Treasury Stock	(2,349.3)	(2,030.7)
Total Stockholders' Equity	8,659.1	8,612.6	8,169.7
Total Liabilities and Stockholders' Equity	59,403.6	62,236.1
Parent Company
Assets [Abstract]
Fixed Maturity Securities	145.3	224.6
Other Long-term Investments	57.2	73.0
Short-term Investments	164.0	433.5
Investments in Subsidiaries	10,082.8	10,079.1
Deferred Income Tax	68.1	234.1
Other Assets	558.8	489.1
Total Assets	11,076.2	11,533.4
Liabilities
Short-term Debt	0.3	6.6
Long-term Debt	1,875.2	1,896.2
Pension and Postretirement Benefits	295.3	801.6
Other Liabilities	246.3	216.4
Total Liabilities	2,417.1	2,920.8
Stockholders' Equity
Common Stock	36.1	36.0
Additional Paid-in Capital	2,634.1	2,607.7
Accumulated Other Comprehensive Income	255.0	628.0
Retained Earnings	8,083.2	7,371.6
Treasury Stock	(2,349.3)	(2,030.7)
Total Stockholders' Equity	8,659.1	8,612.6
Total Liabilities and Stockholders' Equity	$ 11,076.2	$ 11,533.4