Schedule of Income subject to domestic and foreign taxation (Detail) - USD ($) $ in Millions	3 Months Ended								12 Months Ended
	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2015	Sep. 30, 2015	Jun. 30, 2015	Mar. 31, 2015	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Income Tax [Abstract]
Income Before Tax United States - Federal and State									$ 1,215.8	$ 1,057.8	$ 391.7
Income Before Tax Foreign									131.9	180.5	150.3
Income Before Income Tax	$ 371.2	$ 332.1	$ 340.2	$ 304.2	$ 316.6	$ 298.9	$ 319.8	$ 303.0	1,347.7	1,238.3	542.0
Current Tax Expense United States - Federal									414.8	280.5	160.6
Current State and Local Tax Expense (Benefit)									0.3	0.0	0.0
Current Tax Expense Foreign									(29.4)	61.6	(25.1)
Income Tax - Current									385.7	342.1	135.5
Deferred Tax Expense (Benefit) United States - Federal									(14.6)	56.9	(50.5)
Deferred State and Local Income Tax Expense (Benefit)									(2.1)	0.0	0.0
Deferred Tax Expense (Benefit) Foreign									47.3	(27.8)	54.9
Income Tax - Deferred									30.6	29.1	4.4
Income Tax Expense									$ 416.3	$ 371.2	$ 139.9