Parent Company Statement of Income (Detail) (USD $) In Millions, unless otherwise specified	3 Months Ended								12 Months Ended
	Dec. 31, 2013	Sep. 30, 2013	Jun. 30, 2013	Mar. 31, 2013	Dec. 31, 2012	Sep. 30, 2012	Jun. 30, 2012	Mar. 31, 2012	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011
Condensed Financial Statements, Captions [Line Items]
Other Income									$ 230.2	$ 227.9	$ 249.1
Total Revenue	2,586.2	2,540.9	2,601.9	2,624.8	2,658.2	2,628.0	2,617.9	2,611.3	10,353.8	10,515.4	10,278.0
Income Before Income Tax	305.8	284.1	311.5	303.8	322.7	320.4	296.4	310.0	1,205.2	1,249.5	333.3
Income Tax Expense (Benefit)									347.1	355.1	49.1
Net Income	221.2	205.7	218.6	212.6	233.9	230.2	216.4	213.9	858.1	894.4	284.2
Total Other Comprehensive Income (Loss)									(373.0)	166.2	110.4
Comprehensive Income									485.1	1,060.6	394.6
Parent Company
Condensed Financial Statements, Captions [Line Items]
Cash Dividends from Subsidiaries									636.6	670.8	800.0
Other Income									56.9	55.0	65.0
Total Revenue									693.5	725.8	865.0
Interest and Debt Expense									120.9	114.2	112.1
Other Expenses									48.9	65.5	57.7
Total Expenses									169.8	179.7	169.8
Income Before Income Tax									523.7	546.1	695.2
Income Tax Expense (Benefit)									(14.7)	(25.7)	(13.9)
Income of Parent Company									538.4	571.8	709.1
Equity in Undistibuted Earnings (Loss) of Subsidiaries									319.7	322.6	(424.9)
Net Income									858.1	894.4	284.2
Total Other Comprehensive Income (Loss)									(373.0)	166.2	110.4
Comprehensive Income									$ 485.1	$ 1,060.6	$ 394.6