Derivatives - Schedule of Gains (Losses) for Derivatives Designated as Fair Value Hedges (Detail) - USD ($) $ in Millions	3 Months Ended	9 Months Ended
Sep. 30, 2016	Sep. 30, 2016
Derivative Instruments Gain Loss [Line Items]
(Gain) loss recognized as ineffectiveness	$ (0.7)	$ (0.4)
Interest Rate Swap \| Investment and other income-net \| Designated Fair Value Hedges
Derivative Instruments Gain Loss [Line Items]
(Gain) loss recognized as ineffectiveness	3.6	0.4
Hedged Items \| Investment and other income-net \| Designated Fair Value Hedges
Derivative Instruments Gain Loss [Line Items]
(Gain) loss recognized as ineffectiveness	$ (4.3)	$ (0.8)

The portion of gains and losses (net) on derivative instruments designated and qualifying as hedging instruments representing (a) the amount of the hedge ineffectiveness and (b) the amount, if any, excluded from the assessment of hedge effectiveness.

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 815
-SubTopic 10
-Section 50
-Paragraph 4C
-Subparagraph (d)
-URI http://asc.fasb.org/extlink&oid=84234895&loc=SL5624171-113959

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 815
-SubTopic 25
-Section 50
-Paragraph 1
-Subparagraph (a)(1),(2)
-URI http://asc.fasb.org/extlink&oid=6886632&loc=d3e76258-113986

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Period Type:	duration