Other Operating Income - (Detail) - USD ($) shares in Millions, $ in Millions	1 Months Ended		12 Months Ended
	Jun. 30, 2016	Jun. 30, 2015	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Components of Other Operating Income [Line Items]
Total Other Operating Income			$ 127.5	$ 157.5	$ 241.2
Visa Class B
Components of Other Operating Income [Line Items]
Net gain on sale of derivative	$ 123.1	$ 99.9			$ 123.1
Shares sold (in shares)	1.1	1.0			1.1
Loan Service Fees
Components of Other Operating Income [Line Items]
Total Other Operating Income			48.9	50.7	$ 56.6
Banking Service Fees
Components of Other Operating Income [Line Items]
Total Other Operating Income			46.4	48.6	50.6
Other Income
Components of Other Operating Income [Line Items]
Total Other Operating Income			$ 32.2	$ 58.2	$ 134.0