Reporting Segments and Related Information - Distribution of Total Assets and Operating Performance (Detail) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Segment Reporting Information [Line Items]
TOTAL ASSETS	$ 132,212.5	$ 138,590.5	$ 123,926.9
TOTAL REVENUE	5,960.2	5,375.3	4,961.8
INCOME BEFORE INCOME TAXES	1,957.8	1,633.9	1,517.1
Net Income	1,556.4	1,199.0	1,032.5
Non-U.S.
Segment Reporting Information [Line Items]
TOTAL ASSETS	32,712.9	30,325.3	24,944.0
TOTAL REVENUE	2,018.1	1,709.7	1,221.2
INCOME BEFORE INCOME TAXES	786.4	613.5	284.3
Net Income	625.7	430.0	225.1
U.S.
Segment Reporting Information [Line Items]
TOTAL ASSETS	99,499.6	108,265.2	98,982.9
TOTAL REVENUE	3,942.1	3,665.6	3,740.6
INCOME BEFORE INCOME TAXES	1,171.4	1,020.4	1,232.8
Net Income	$ 930.7	$ 769.0	$ 807.4