Insurance In Force (Schedule Of Insurance In Force By Type Of Bond, Excluding Transactions Guaranteed By MBIA Corp. On Behalf Of Various Investment Management Services And Other Affiliated Companies) (Parenthetical) (Detail) - USD ($) $ in Billions	Dec. 31, 2019	Dec. 31, 2018
Insurance in Force	$ 107.5	$ 128.1
Gross Par Amount	58.9	69.8
Corporate Asset Backed [Member] | Structured Insurance Securitizations [Member]
Insurance in Force	2.1	2.2
Gross Par Amount	$ 1.0	$ 1.0