Subsequent Event (Subsequent Event - Additional Information) (Detail) $ in Millions	3 Months Ended	9 Months Ended
Sep. 30, 2017 USD ($)	Sep. 30, 2017 USD ($)
Subsequent Event
Face amount of notes issued or redeemed	$ 700.0	$ 700.0
Maturity date(s) Start		Jun. 15, 2017
Maturity date(s) End		Jun. 15, 2022
Subsequent Event
Subsequent Event
Subsequent Event Date		Oct. 30, 2017
Senior Notes Due 2020
Subsequent Event
Face amount of notes issued or redeemed	$ 1,100.0	$ 1,100.0
Maturity date(s) Start	Oct. 30, 2017
Maturity date(s) End	Oct. 30, 2020
Fixed Rate 2.20 Percent Senior Notes Due 2020
Subsequent Event
Face amount of notes issued or redeemed	$ 750.0	750.0
Floating Rate 3ML Plus 25 bps Senior Notes Due 2020
Subsequent Event
Face amount of notes issued or redeemed	$ 300.0	$ 300.0

Face (par) amount of debt instrument at time of issuance.

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 835
-SubTopic 30
-Section 55
-Paragraph 8
-URI http://asc.fasb.org/extlink&oid=64930739&loc=d3e28878-108400

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 835
-SubTopic 30
-Section 45
-Paragraph 2
-URI http://asc.fasb.org/extlink&oid=64930785&loc=d3e28551-108399

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Latest date the outstanding debt instruments are required to be repaid, in CCYY-MM-DD format.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 210
-SubTopic 10
-Section S99
-Paragraph 1
-Subparagraph (SX 210.5-02.22(a)(2))
-URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682

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Earliest date the outstanding debt instruments are required to be repaid, in CCYY-MM-DD format.

+ References

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- Definition

Detail information of subsequent event by type. User is expected to use existing line items from elsewhere in the taxonomy as the primary line items for this disclosure, which is further associated with dimension and member elements pertaining to a subsequent event.

+ References

No definition available.

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Date the event occurred after the balance sheet date but before financial statements are issues or available to be issued, in CCYY-MM-DD format.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 855
-SubTopic 10
-Section 50
-Paragraph 2
-Subparagraph (a)
-URI http://asc.fasb.org/extlink&oid=6842918&loc=SL6314017-165662

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