Long Term Debt (Long Term Debt - Additional Information) (Detail) - Subsidiaries $ in Millions	6 Months Ended
Jun. 30, 2016 USD ($)
Debt Instrument
Issue of senior notes to third party investors	$ 1,500
Senior Debt Obligations \| Fixed Rate 2.30 Percent Notes Due 2019
Debt Instrument
Issue of senior notes to third party investors	$ 750
Maturity date(s) Start	Mar. 15, 2016
Maturity date(s) End	Mar. 15, 2019
Senior Debt Obligations \| Fixed Rate 2.25 Percent Notes Due 2021
Debt Instrument
Issue of senior notes to third party investors	$ 1,300
Maturity date(s) Start	Jun. 14, 2016
Maturity date(s) End	Jun. 14, 2021
Subordinated Debt \| Fixed Rate 3.85 Percent Notes Due 2026
Debt Instrument
Issue of senior notes to third party investors	$ 750
Maturity date(s) Start	Mar. 15, 2016
Maturity date(s) End	Mar. 15, 2026

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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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.

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