Reporting Segments and Related Information - Distribution of Total Assets and Operating Performance (Detail) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Segment Reporting Information [Line Items]
TOTAL ASSETS	$ 138,590.5	$ 123,926.9	$ 116,749.6
TOTAL REVENUE	5,375.3	4,961.8	4,702.6
INCOME BEFORE INCOME TAXES	1,633.9	1,517.1	1,465.0
Net Income	1,199.0	1,032.5	973.8
Non - U.S.
Segment Reporting Information [Line Items]
TOTAL ASSETS	30,325.3	24,944.0	30,636.5
TOTAL REVENUE	1,709.7	1,221.2	1,358.4
INCOME BEFORE INCOME TAXES	613.5	284.3	483.2
Net Income	430.0	225.1	344.4
U.S.
Segment Reporting Information [Line Items]
TOTAL ASSETS	108,265.2	98,982.9	86,113.1
TOTAL REVENUE	3,665.6	3,740.6	3,344.2
INCOME BEFORE INCOME TAXES	1,020.4	1,232.8	981.8
Net Income	$ 769.0	$ 807.4	$ 629.4