Insurance Regulations And Dividends (Narrative) (Detail) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2022	Dec. 31, 2021	Dec. 31, 2020
Insurance Regulations And Dividends [Line Items]
Percentage of policyholders' surplus	10.00%
Percentage of adjusted net investment income	100.00%
Policyholders Surplus [Member] | Minimum [Member]
Insurance Regulations And Dividends [Line Items]
Policyholders' surplus	$ 65
MBIA Corp [Member]
Insurance Regulations And Dividends [Line Items]
Unassigned surplus	1,900	$ 1,900
Statutory net loss		129	$ 202
Statutory capital	169	134
Policyholders' surplus	164
Contingency reserves	5
Statutory net income	46
National [Member]
Insurance Regulations And Dividends [Line Items]
Dividends from subsidiaries	72	60	81
Statutory net loss			$ 82
Statutory capital	1,900	2,000
Policyholders' surplus	1,500
Contingency reserves	379
Statutory net income	$ 75	$ 55