Other Operating Income - (Detail) - USD ($) $ in Millions	1 Months Ended		12 Months Ended
	Jun. 30, 2016	Jun. 30, 2015	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Components of Other Operating Income [Line Items]
Loan Service Fees			$ 50.7	$ 56.6	$ 59.1
Banking Service Fees			48.6	50.6	48.2
Other Income			58.2	134.0	139.8
Total Other Operating Income			$ 157.5	241.2	247.1
Visa Class B
Components of Other Operating Income [Line Items]
Net gain on sale of derivative	$ 123.1	$ 99.9		$ 123.1	$ 99.9
Shares sold (in shares)	1,100,000	1,000,000		1,100,000.0	1,000,000.0