Balance Sheet Offsetting - Summary of Gross Presentation, Financial Instruments that are Eligible for Offset in Consolidated Statement of Condition (Detail) - USD ($) $ in Millions	Dec. 31, 2019	Dec. 31, 2018
Financial assets:
Gross Amount Recognized	$ 18.4	$ 26.0
Gross Amount Offset	0.0	0.0
Net Amount Presented	18.4	26.0
Gross amounts not offset, financial instruments	(1.9)	(15.7)
Gross amounts not offset, collateral	0.0	(8.6)
Net Amount	16.5	1.7
Financial liabilities:
Gross Amount Recognized	81.6	33.8
Gross Amount Offset	0.0	0.0
Net Amount Presented	81.6	33.8
Gross amounts not offset, financial instruments	(1.9)	(15.7)
Gross amounts not offset, collateral	(77.9)	(1.2)
Net Amount	1.8	16.9
Interest Rate Swaps/Caps [Member]
Financial assets:
Gross Amount Offset	0.0
Foreign Exchange Contracts [Member]
Financial assets:
Gross Amount Recognized	1.2	0.9
Gross Amount Offset	0.0	0.0
Net Amount Presented	1.2	0.9
Gross amounts not offset, financial instruments	0.0	0.0
Gross amounts not offset, collateral	0.0	0.0
Net Amount	1.2	0.9
Financial liabilities:
Gross Amount Recognized	1.8	0.8
Gross Amount Offset	0.0	0.0
Net Amount Presented	1.8	0.8
Gross amounts not offset, financial instruments	0.0	0.0
Gross amounts not offset, collateral	0.0	0.0
Net Amount	1.8	0.8
Counterparty A [Member] | Interest Rate Swaps/Caps [Member]
Financial assets:
Gross Amount Recognized	0.2	3.1
Gross Amount Offset	0.0	0.0
Net Amount Presented	0.2	3.1
Gross amounts not offset, financial instruments	(0.2)	(1.4)
Gross amounts not offset, collateral	0.0	(1.7)
Net Amount	0.0	0.0
Financial liabilities:
Gross Amount Recognized	2.3	1.4
Gross Amount Offset	0.0	0.0
Net Amount Presented	2.3	1.4
Gross amounts not offset, financial instruments	(0.2)	(1.4)
Gross amounts not offset, collateral	(2.1)	0.0
Net Amount	0.0	0.0
Counterparty B [Member] | Interest Rate Swaps/Caps [Member]
Financial assets:
Gross Amount Recognized	0.1	2.5
Gross Amount Offset	0.0	0.0
Net Amount Presented	0.1	2.5
Gross amounts not offset, financial instruments	(0.1)	(2.5)
Gross amounts not offset, collateral	0.0	0.0
Net Amount	0.0	0.0
Financial liabilities:
Gross Amount Recognized	5.5	3.8
Gross Amount Offset	0.0	0.0
Net Amount Presented	5.5	3.8
Gross amounts not offset, financial instruments	(0.1)	(2.5)
Gross amounts not offset, collateral	(5.4)	(1.2)
Net Amount	0.0	0.1
Counterparty C [Member] | Interest Rate Swaps/Caps [Member]
Financial assets:
Gross Amount Recognized	0.4	4.8
Gross Amount Offset	0.0	0.0
Net Amount Presented	0.4	4.8
Gross amounts not offset, financial instruments	(0.4)	(3.7)
Gross amounts not offset, collateral	0.0	(1.1)
Net Amount	0.0	0.0
Financial liabilities:
Gross Amount Recognized	28.2	3.7
Gross Amount Offset	0.0	0.0
Net Amount Presented	28.2	3.7
Gross amounts not offset, financial instruments	(0.4)	(3.7)
Gross amounts not offset, collateral	(27.8)	0.0
Net Amount	0.0	0.0
Counterparty D [Member] | Interest Rate Swaps/Caps [Member]
Financial assets:
Gross Amount Recognized	0.1	3.6
Gross Amount Offset	0.0	0.0
Net Amount Presented	0.1	3.6
Gross amounts not offset, financial instruments	(0.1)	(2.7)
Gross amounts not offset, collateral	0.0	(0.1)
Net Amount	0.0	0.8
Financial liabilities:
Gross Amount Recognized	10.9	2.7
Gross Amount Offset	0.0	0.0
Net Amount Presented	10.9	2.7
Gross amounts not offset, financial instruments	(0.1)	(2.7)
Gross amounts not offset, collateral	(10.8)	0.0
Net Amount	0.0	0.0
Counterparty E [Member] | Interest Rate Swaps/Caps [Member]
Financial assets:
Gross Amount Recognized	15.3	0.0
Gross Amount Offset		0.0
Net Amount Presented	15.3	0.0
Gross amounts not offset, financial instruments	0.0	0.0
Gross amounts not offset, collateral	0.0	0.0
Net Amount	15.3	0.0
Financial liabilities:
Gross Amount Recognized	0.0	16.0
Gross Amount Offset	0.0	0.0
Net Amount Presented	0.0	16.0
Gross amounts not offset, financial instruments	0.0	0.0
Gross amounts not offset, collateral	0.0	0.0
Net Amount	0.0	16.0
Other Counterparties [Member] | Interest Rate Swaps/Caps [Member]
Financial assets:
Gross Amount Recognized	1.1	11.1
Gross Amount Offset	0.0	0.0
Net Amount Presented	1.1	11.1
Gross amounts not offset, financial instruments	(1.1)	(5.4)
Gross amounts not offset, collateral	0.0	(5.7)
Net Amount	0.0	0.0
Financial liabilities:
Gross Amount Recognized	32.9	5.4
Gross Amount Offset	0.0	0.0
Net Amount Presented	32.9	5.4
Gross amounts not offset, financial instruments	(1.1)	(5.4)
Gross amounts not offset, collateral	(31.8)	0.0
Net Amount	$ 0.0	$ 0.0