Distribution of Total Assets and Operating Performance (Detail) (USD $) In Millions, unless otherwise specified	12 Months Ended
	Dec. 31, 2014		Dec. 31, 2013		Dec. 31, 2012
Geographic Reporting Disclosure [Line Items]
Total Assets	$ 109,946.5		$ 102,947.3		$ 97,463.8
Total Revenue	4,331.2	[1]	4,089.3	[1]	3,896.1	[1]
Income Before Income Taxes	1,190.2		1,075.5		992.3
Net Income	811.8		731.3		687.3
Non - U.S.
Geographic Reporting Disclosure [Line Items]
Total Assets	28,326.1		30,241.3		29,198.4
Total Revenue	1,341.8	[1]	1,101.0	[1]	992.5	[1]
Income Before Income Taxes	446.5		272.4		194.9
Net Income	322.7		201.3		147.6
U.S.
Geographic Reporting Disclosure [Line Items]
Total Assets	81,620.4		72,706.0		68,265.4
Total Revenue	2,989.4	[1]	2,988.3	[1]	2,903.6	[1]
Income Before Income Taxes	743.7		803.1		797.4
Net Income	$ 489.1		$ 530.0		$ 539.7

[1] Total revenue is comprised of net interest income and noninterest income.