Schedule of Income subject to domestic and foreign taxation (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
Income Before Tax United States - Federal									$ 1,072.0	$ 1,128.4	$ 160.5
Income Before Tax Foreign									133.2	121.1	172.8
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
Current Tax Expense United States - Federal									277.9	164.4	218.4
Current Tax Expense Foreign									18.7	42.2	12.1
Current Tax Expense Total									296.6	206.6	230.5
Deferred Tax Expense (Benefit) United States - Federal									47.3	173.5	(203.4)
Deferred Tax Expense (Benefit) Foreign									3.2	(25.0)	22.0
Income Tax (Benefit) - Deferred									50.5	148.5	(181.4)
Income Tax Expense (Benefit)									$ 347.1	$ 355.1	$ 49.1