Derivative Instruments (Total Fair Value Of Company's Derivative Assets And Liabilities By Instrument And Balance Sheet Location, Before Counterparty Netting) (Detail) - Not Designated as Hedging Instrument [Member] - Derivative Instrument [Member] - USD ($) $ in Millions		Dec. 31, 2020	Dec. 31, 2019
Derivative [Line Items]
Derivative notional amount		$ 2,534	$ 2,737
Derivative Assets, Not designated, Fair Value	[1]	7	9
Derivative Liabilities, Not designated, Fair Value	[1]	(225)	(190)
Insured credit default swaps [Member]
Derivative [Line Items]
Derivative notional amount			32
Insured credit default swaps [Member] | Other assets [Member]
Derivative [Line Items]
Derivative Assets, Not designated, Fair Value	[1]		0
Insured credit default swaps [Member] | Derivative liabilities [Member]
Derivative [Line Items]
Derivative Liabilities, Not designated, Fair Value	[1]		(7)
Insured swaps [Member]
Derivative [Line Items]
Derivative notional amount		1,743	1,925	[2]
Insured swaps [Member] | Other assets [Member]
Derivative [Line Items]
Derivative Assets, Not designated, Fair Value	[1]	0	0
Insured swaps [Member] | Derivative liabilities [Member]
Derivative [Line Items]
Derivative Liabilities, Not designated, Fair Value	[1]	(2)	(2)
Interest rate swaps [Member]
Derivative [Line Items]
Derivative notional amount		437	441
Interest rate swaps [Member] | Other assets [Member]
Derivative [Line Items]
Derivative Assets, Not designated, Fair Value	[1]	1	1
Interest rate swaps [Member] | Derivative liabilities [Member]
Derivative [Line Items]
Derivative Liabilities, Not designated, Fair Value	[1]	(164)	(132)
Interest rate swaps-embedded [Member]
Derivative [Line Items]
Derivative notional amount		252	232
Interest rate swaps-embedded [Member] | Medium-term notes [Member]
Derivative [Line Items]
Derivative Assets, Not designated, Fair Value	[1]	0	0
Derivative Liabilities, Not designated, Fair Value	[1]	(10)	(15)
Currency swaps-VIE [Member]
Derivative [Line Items]
Derivative notional amount		53	58
Currency swaps-VIE [Member] | Other assets-VIE [Member]
Derivative [Line Items]
Derivative Assets, Not designated, Fair Value	[1]	6	8
Currency swaps-VIE [Member] | Derivative liabilities-VIE [Member]
Derivative [Line Items]
Derivative Liabilities, Not designated, Fair Value	[1]	0	0
All other [Member]
Derivative [Line Items]
Derivative notional amount		49	49
All other [Member] | Other assets [Member]
Derivative [Line Items]
Derivative Assets, Not designated, Fair Value	[1]	0	0
All other [Member] | Derivative liabilities [Member]
Derivative [Line Items]
Derivative Liabilities, Not designated, Fair Value	[1]	$ (49)	$ (34)

[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.

[2] The Company revised its previously reported amount of $1,795 million to $1,925 million.