Debt (Principal Payments For Investment Agreements, MTNs and VIE Obligations) (Detail) - USD ($) $ in Millions		12 Months Ended
		Dec. 31, 2019	Dec. 31, 2018
Debt Instrument [Line Items]
Accrued interest		$ 877	$ 751
Investment Agreement Obligations [Member]
Debt Instrument [Line Items]
2020		36
2021		2
2022		2
2023		20
2024		26
Thereafter		262
Total expected principal payments	[1]	348
Less discount and other adjustments	[2]	44
Total		304
Accrued interest		5
Carrying amount and market value adjustment		$ 3
Latest maturity year		2037
Medium-term notes [Member]
Debt Instrument [Line Items]
2020		$ 0
2021		0
2022		57
2023		12
2024		113
Thereafter		705
Total expected principal payments	[3]	887
Less discount and other adjustments	[4]	207
Total		680
Accrued interest		4
Carrying amount and market value adjustment		$ 43
Latest maturity year		2036
Variable Interest Entity Debt [Member] | International And Structured Finance Insurance [Member]
Debt Instrument [Line Items]
Latest maturity year		2052
Variable Interest Entity Debt [Member] | MBIA insured Variable Interest Entity [Member]
Debt Instrument [Line Items]
2020		$ 59
2021		64
2022		291
2023		12
2024		12
Thereafter		1,174
Total expected principal payments		$ 1,612

[1] Amounts reflect principal due at maturity for investment agreements issued at a discount.

[2] Discount is net of carrying amount adjustment of $4 million and accrued interest adjustment of $5 million.

[3] Amounts reflect principal due at maturity for notes issued at a discount.

[4] Discount is net of carrying amount adjustment of $34 million and accrued interest adjustment of $5 million.