Additional Information about Derivative Assets and Liabilities Subject to Enforceable Master Netting Arrangement (Detail) - USD ($) $ in Millions	Dec. 31, 2019	Dec. 31, 2018
Derivative [Line Items]
Gross amounts recognized, derivatives assets	$ 310	$ 117
Gross amounts recognized, derivatives liabilities	805	847
Subject to enforceable master netting arrangement
Derivative [Line Items]
Gross amounts recognized, net derivatives	280	(12)
Gross amounts offset in the balance sheet, net derivatives	0	0
Net amounts presented in the balance sheet, net derivatives	280	(12)
Gross amounts not offset in the balance sheet, financial instruments, net derivatives	0	0
Collateral received	(179)	(54)
Collateral pledged	405	535
Over collateralization, net derivatives	(383)	(434)
Net amount	123	35
Subject to enforceable master netting arrangement | Derivative assets
Derivative [Line Items]
Gross amounts recognized, derivatives assets	291	97
Gross amounts offset in the balance sheet, derivatives assets	0	0
Net amounts presented in the balance sheet, derivatives assets	291	97
Gross amounts not offset in the balance sheet, financial instruments, derivatives assets	(7)	(8)
Collateral received	(179)	(54)
Collateral pledged	0	0
Over collateralization, derivatives assets	18	0
Net amount, derivatives assets	123	35
Subject to enforceable master netting arrangement | Derivative liabilities
Derivative [Line Items]
Gross amounts recognized, derivatives liabilities	11	109
Gross amounts offset in the balance sheet, derivatives liabilities	0	0
Net amounts presented in the balance sheet, derivatives liabilities	11	109
Gross amounts not offset in the balance sheet, financial instruments, derivative liabilities	(7)	(8)
Collateral received	0	0
Collateral pledged	(405)	(535)
Over collateralization, derivatives liabilities	401	434
Net amount, derivatives liabilities	$ 0	$ 0