Reporting Segments and Related Information - Distribution of Total Assets and Operating Performance (Detail) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Segment Reporting Information [Line Items]
TOTAL ASSETS	$ 136,828.4	$ 132,212.5	$ 138,590.5
TOTAL REVENUE	6,073.1	5,960.2	5,375.3
INCOME BEFORE INCOME TAXES	1,944.1	1,957.8	1,633.9
Net Income	1,492.2	1,556.4	1,199.0
Non-U.S.
Segment Reporting Information [Line Items]
TOTAL ASSETS	27,888.6	32,712.9	30,325.3
TOTAL REVENUE	1,889.5	2,018.1	1,709.7
INCOME BEFORE INCOME TAXES	600.0	786.4	613.5
Net Income	451.0	625.7	430.0
U.S.
Segment Reporting Information [Line Items]
TOTAL ASSETS	108,939.8	99,499.6	108,265.2
TOTAL REVENUE	4,183.6	3,942.1	3,665.6
INCOME BEFORE INCOME TAXES	1,344.1	1,171.4	1,020.4
Net Income	$ 1,041.2	$ 930.7	$ 769.0