Long Term Debt (Long Term Debt - Additional Information) (Detail) - Subsidiaries $ in Millions	9 Months Ended
Sep. 30, 2016 USD ($)
March 2016 Issuance
Debt Instrument
Face amount of notes issued or redeemed	$ 1,500
Senior Debt Obligations \| September 2016 Issuance
Debt Instrument
Face amount of notes issued or redeemed	1,000
Senior Debt Obligations \| Fixed Rate 2.30 Percent Notes Due 2019 \| March 2016 Issuance
Debt Instrument
Face amount of notes issued or redeemed	$ 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 \| June 2016 Issuance
Debt Instrument
Face amount of notes issued or redeemed	$ 1,300
Maturity date(s) Start	Jun. 14, 2016
Maturity date(s) End	Jun. 14, 2021
Senior Debt Obligations \| Fixed Rate 1.625 Percent Notes Due 2019 \| September 2016 Issuance
Debt Instrument
Face amount of notes issued or redeemed	$ 750
Maturity date(s) Start	Sep. 27, 2016
Maturity date(s) End	Sep. 27, 2019
Senior Debt Obligations \| Floating Rate 3 Month LIBOR Plus 59 bps Notes Due 2019 \| September 2016 Issuance
Debt Instrument
Face amount of notes issued or redeemed	$ 250
Maturity date(s) Start	Sep. 27, 2016
Maturity date(s) End	Sep. 27, 2019
Senior Debt Obligations \| Fixed Rate 1.15 Percent Notes Due 2016 \| September 2016 Redemption
Debt Instrument
Face amount of notes issued or redeemed	$ 1,000
Maturity date(s) End	Nov. 18, 2016
Redemption date(s) Start	Sep. 02, 2016
Redemption date(s) End	Oct. 19, 2016
Senior Debt Obligations \| Floating Rate 3 Month LIBOR Plus 51 bps Notes Due 2016 \| September 2016 Redemption
Debt Instrument
Face amount of notes issued or redeemed	$ 750
Maturity date(s) End	Nov. 18, 2016
Redemption date(s) Start	Sep. 02, 2016
Redemption date(s) End	Oct. 19, 2016
Subordinated Debt \| Fixed Rate 3.85 Percent Notes Due 2026 \| March 2016 Issuance
Debt Instrument
Face amount of notes issued or redeemed	$ 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=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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+ 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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+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 942
-SubTopic 470
-Section 50
-Paragraph 3
-Subparagraph e
-URI http://asc.fasb.org/extlink&oid=6479336&loc=d3e64711-112823

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