Financial Instruments - Additional Information (Detail) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Schedule of Cost-method Investments [Line Items]
Derivative Instruments, Gain (Loss) Reclassification from Accumulated OCI to Income, Estimated Net Amount to be Transferred	$ 5
Interest Rate Swap [Member]
Schedule of Cost-method Investments [Line Items]
Derivative, Notional Amount		$ 900	$ 0
Interest Rate Caps [Member]
Schedule of Cost-method Investments [Line Items]
Derivative, Notional Amount		10,179	0
Interest Rate Caps [Member] | Interest Rate Caps Sold
Schedule of Cost-method Investments [Line Items]
Derivative, Notional Amount		8,200	6,200
Interest Rate Caps [Member] | Interest Rate Caps Purchased
Schedule of Cost-method Investments [Line Items]
Derivative, Notional Amount		2,000	2,100
Interest Rate Caps [Member] | Interest Rate Caps Purchased | Subsidiary Issuers
Schedule of Cost-method Investments [Line Items]
Derivative, Notional Amount		6,200	4,200
Currency Swap [Member]
Schedule of Cost-method Investments [Line Items]
Derivative, Notional Amount		$ 811	$ 0