Derivative Instruments (Total Fair Value Of Company's Derivative Assets And Liabilities By Instrument And Balance Sheet Location, Before Counterparty Netting) (Detail) - Derivative Instrument [Member] - Not Designated as Hedging Instrument [Member] - USD ($) $ in Millions		Sep. 30, 2019	Dec. 31, 2018
Derivative [Line Items]
Derivative notional amount		$ 2,628	$ 3,619
Derivative Assets, Not designated, Fair Value	[1]	10	18
Derivative Liabilities, Not designated, Fair Value	[1]	(211)	(212)
Interest Rate Swaps [Member]
Derivative [Line Items]
Derivative notional amount		440	712
Credit Default Swap [Member]
Derivative [Line Items]
Derivative notional amount		34	70
Insured Swaps [Member]
Derivative [Line Items]
Derivative notional amount		1,822	2,433
Interest Rate Swaps Embedded [Member]
Derivative [Line Items]
Derivative notional amount		227	293
Currency swaps-VIE [Member]
Derivative [Line Items]
Derivative notional amount		56	62
All Other [Member]
Derivative [Line Items]
Derivative notional amount		49	49
Derivative Liabilities [Member] | Interest Rate Swaps [Member]
Derivative [Line Items]
Derivative Liabilities, Not designated, Fair Value	[1]	(152)	(157)
Derivative Liabilities [Member] | Credit Default Swap [Member]
Derivative [Line Items]
Derivative Liabilities, Not designated, Fair Value	[1]	(10)	(33)
Derivative Liabilities [Member] | Insured Swaps [Member]
Derivative [Line Items]
Derivative Liabilities, Not designated, Fair Value	[1]	(2)	(2)
Derivative Liabilities [Member] | All Other [Member]
Derivative [Line Items]
Derivative Liabilities, Not designated, Fair Value	[1]	(30)	(7)
Medium-term Notes [Member] | Interest Rate Swaps Embedded [Member]
Derivative [Line Items]
Derivative Assets, Not designated, Fair Value	[1]	0
Derivative Liabilities, Not designated, Fair Value	[1]	(17)	(13)
Other Assets [Member] | Interest Rate Swaps [Member]
Derivative [Line Items]
Derivative Assets, Not designated, Fair Value	[1]	2	2
Other Assets [Member] | Credit Default Swap [Member]
Derivative [Line Items]
Derivative Assets, Not designated, Fair Value	[1]	0
Other Assets [Member] | Insured Swaps [Member]
Derivative [Line Items]
Derivative Assets, Not designated, Fair Value	[1]	0
Other Assets [Member] | All Other [Member]
Derivative [Line Items]
Derivative Assets, Not designated, Fair Value	[1]	0
Other Assets V I E [Member] | Currency swaps-VIE [Member]
Derivative [Line Items]
Derivative Assets, Not designated, Fair Value	[1]	8	$ 16
Derivative Liabilities V I E [Member] | Currency swaps-VIE [Member]
Derivative [Line Items]
Derivative Liabilities, Not designated, Fair Value	[1]	$ 0

[1] In accordance with the accounting guidance for derivative instruments and hedging activities, the balance sheet location of the Company’s embedded derivative instruments is determined by the location of the related host contract.