Fair Value Measurements - Valuation of Financial Instruments that are Marked-to-Market on Recurring Basis (Detail) - USD ($) $ in Millions	Sep. 30, 2016	Dec. 31, 2015
Available-for-sale investments:
Available-for-sale investments	$ 4	$ 5
Derivative assets	949	728
Derivative liabilities	(1,318)	(1,515)
Interest Rate Swaps [Member]
Available-for-sale investments:
Derivative assets	930	726
Derivative liabilities	(272)	(160)
Cross-Currency Interest Rate Swaps [Member]
Available-for-sale investments:
Derivative assets	18	2
Derivative liabilities	(742)	(988)
Other [Member]
Available-for-sale investments:
Derivative assets	1
Derivative liabilities	(11)	(2)
Floor Income Contracts [Member]
Available-for-sale investments:
Derivative liabilities	(293)	(365)
Fair Value Measurements Recurring [Member]
Available-for-sale investments:
Available-for-sale investments	4	5
Derivative assets	949	728
Total	953	733
Derivative liabilities	(1,318)	(1,515)
Total	(1,318)	(1,515)
Fair Value Measurements Recurring [Member] \| Interest Rate Swaps [Member]
Available-for-sale investments:
Derivative assets	930	726
Derivative liabilities	(272)	(160)
Fair Value Measurements Recurring [Member] \| Cross-Currency Interest Rate Swaps [Member]
Available-for-sale investments:
Derivative assets	18	2
Derivative liabilities	(742)	(988)
Fair Value Measurements Recurring [Member] \| Other [Member]
Available-for-sale investments:
Derivative assets	1
Derivative liabilities	(11)	(2)
Fair Value Measurements Recurring [Member] \| Floor Income Contracts [Member]
Available-for-sale investments:
Derivative liabilities	(293)	(365)
Fair Value Measurements Recurring [Member] \| Agency Residential Mortgage-Backed Securities [Member]
Available-for-sale investments:
Available-for-sale investments	1	1
Fair Value Measurements Recurring [Member] \| Other [Member]
Available-for-sale investments:
Available-for-sale investments	3	4
Level 2 [Member] \| Fair Value Measurements Recurring [Member]
Available-for-sale investments:
Available-for-sale investments	4	5
Derivative assets	904	709
Total	908	714
Derivative liabilities	(510)	(547)
Total	(510)	(547)
Level 2 [Member] \| Fair Value Measurements Recurring [Member] \| Interest Rate Swaps [Member]
Available-for-sale investments:
Derivative assets	904	709
Derivative liabilities	(207)	(99)
Level 2 [Member] \| Fair Value Measurements Recurring [Member] \| Cross-Currency Interest Rate Swaps [Member]
Available-for-sale investments:
Derivative liabilities	(10)	(83)
Level 2 [Member] \| Fair Value Measurements Recurring [Member] \| Floor Income Contracts [Member]
Available-for-sale investments:
Derivative liabilities	(293)	(365)
Level 2 [Member] \| Fair Value Measurements Recurring [Member] \| Agency Residential Mortgage-Backed Securities [Member]
Available-for-sale investments:
Available-for-sale investments	1	1
Level 2 [Member] \| Fair Value Measurements Recurring [Member] \| Other [Member]
Available-for-sale investments:
Available-for-sale investments	3	4
Level 3 [Member] \| Fair Value Measurements Recurring [Member]
Available-for-sale investments:
Derivative assets	45	19
Total	45	19
Derivative liabilities	(808)	(968)
Total	(808)	(968)
Level 3 [Member] \| Fair Value Measurements Recurring [Member] \| Interest Rate Swaps [Member]
Available-for-sale investments:
Derivative assets	26	17
Derivative liabilities	(65)	(61)
Level 3 [Member] \| Fair Value Measurements Recurring [Member] \| Cross-Currency Interest Rate Swaps [Member]
Available-for-sale investments:
Derivative assets	18	2
Derivative liabilities	(732)	(905)
Level 3 [Member] \| Fair Value Measurements Recurring [Member] \| Other [Member]
Available-for-sale investments:
Derivative assets	1
Derivative liabilities	$ (11)	$ (2)

Fair value portion of probable future economic benefits obtained or controlled by an entity as a result of past transactions or events.

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 820
-SubTopic 10
-Section 50
-Paragraph 2
-Subparagraph (a)
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Amount of investment in debt and equity securities categorized neither as held-to-maturity nor trading.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
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Fair value, before effects of master netting arrangements, of a financial asset or other contract with one or more underlyings, notional amount or payment provision or both, and the contract can be net settled by means outside the contract or delivery of an asset. Includes assets elected not to be offset. Excludes assets not subject to a master netting arrangement.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
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Reference 2: http://www.xbrl.org/2003/role/presentationRef
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Reference 3: http://www.xbrl.org/2003/role/presentationRef
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Reference 1: http://www.xbrl.org/2003/role/presentationRef
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Fair value of financial and nonfinancial obligations.

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