Long Term Debt - Additional Information (Detail) - Senior Debt Obligations $ in Millions	9 Months Ended
Sep. 30, 2015 USD ($)
Parent company \| Fixed rate 2.875 percent senior notes due 2020
Debt Instrument [Line Items]
Issue of senior notes to third party investors	$ 1,100
Maturity date(s) Start	Jul. 27, 2015
Maturity date(s) End	Jul. 27, 2020
Subsidiaries \| Fixed rate 2.15 percent senior notes due 2018
Debt Instrument [Line Items]
Issue of senior notes to third party investors	$ 1,000
Maturity date(s) Start	Aug. 20, 2015
Maturity date(s) End	Aug. 20, 2018
Subsidiaries \| Floating rate 3 Month LIBOR plus 91 bps due 2018
Debt Instrument [Line Items]
Issue of senior notes to third party investors	$ 250
Maturity date(s) Start	Aug. 20, 2015
Maturity date(s) End	Aug. 20, 2018

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=34725769&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=6451184&loc=d3e28551-108399

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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))

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