Derivative Financial Instruments - Impact of Derivatives on Consolidated Balance Sheet (Detail) - USD ($) $ in Millions	Jun. 30, 2019	Dec. 31, 2018
Derivative Assets:
Derivative assets	$ 246	$ 179
Derivative Liabilities:
Derivative liabilities	(731)	(801)
Net total derivatives	(485)	(622)
Designated as Hedging Instrument [Member] | Fair Value [Member]
Derivative Assets:
Derivative assets	242	176
Derivative Liabilities:
Derivative liabilities	(606)	(673)
Net total derivatives	(364)	(497)
Trading [Member]
Derivative Assets:
Derivative assets	4	3
Derivative Liabilities:
Derivative liabilities	(125)	(128)
Net total derivatives	(121)	(125)
Interest Rate Swaps [Member]
Derivative Assets:
Derivative assets	243	173
Derivative Liabilities:
Derivative liabilities	(24)	(79)
Interest Rate Swaps [Member] | Designated as Hedging Instrument [Member] | Fair Value [Member]
Derivative Assets:
Derivative assets	239	170
Derivative Liabilities:
Derivative liabilities		(34)
Interest Rate Swaps [Member] | Trading [Member]
Derivative Assets:
Derivative assets	4	3
Derivative Liabilities:
Derivative liabilities	(24)	(45)
Cross-Currency Interest Rate Swaps [Member]
Derivative Assets:
Derivative assets	3	6
Derivative Liabilities:
Derivative liabilities	(606)	(665)
Cross-Currency Interest Rate Swaps [Member] | Designated as Hedging Instrument [Member] | Fair Value [Member]
Derivative Assets:
Derivative assets	3	6
Derivative Liabilities:
Derivative liabilities	(606)	(639)
Cross-Currency Interest Rate Swaps [Member] | Trading [Member]
Derivative Liabilities:
Derivative liabilities		(26)
Floor Income Contracts [Member]
Derivative Liabilities:
Derivative liabilities	(99)	(53)
Floor Income Contracts [Member] | Trading [Member]
Derivative Liabilities:
Derivative liabilities	(99)	(53)
Other [Member]
Derivative Liabilities:
Derivative liabilities	(2)	(4)
Other [Member] | Trading [Member]
Derivative Liabilities:
Derivative liabilities	$ (2)	$ (4)