Fair Value Of Financial Instruments (Fair Value Hierarchy Table Presents The Company's Assets And Liabilities At Fair Value Not Recorded On The Company's Consolidated Balance Sheet) (Detail) - Value Disclosed At Fair Value Not Recorded At Fair Value [Member] - Fair Value Measurements Nonrecurring [Member] - USD ($) $ in Millions	Mar. 31, 2022	Dec. 31, 2021
Carrying Reported Amount Fair Value Disclosure [Member]
Fair Value Off Balance Sheet Risks Disclosure Information [Line Items]
Long-term debt	$ 2,344	$ 2,331
Medium-term notes	487	490
Investment agreements	274	274
Total liabilities	3,105	3,095
Gross	828	(80)
Ceded recoverable (liability)	17	(42)
Fair Value [Member]
Fair Value Off Balance Sheet Risks Disclosure Information [Line Items]
Long-term debt	413	433
Medium-term notes	329	322
Investment agreements	331	355
Total liabilities	1,073	1,110
Gross	1,214	848
Ceded recoverable (liability)	33	30
Fair Value [Member] | Fair Value Inputs Level 1 [Member]
Fair Value Off Balance Sheet Risks Disclosure Information [Line Items]
Long-term debt	0	0
Medium-term notes	0	0
Investment agreements	0	0
Total liabilities	0	0
Gross	0	0
Ceded recoverable (liability)	0	0
Fair Value [Member] | Fair Value Inputs Level 2 [Member]
Fair Value Off Balance Sheet Risks Disclosure Information [Line Items]
Long-term debt	413	433
Medium-term notes	0	0
Investment agreements	0	0
Total liabilities	413	433
Gross	0	0
Ceded recoverable (liability)	0	0
Fair Value [Member] | Fair Value Inputs Level 3 [Member]
Fair Value Off Balance Sheet Risks Disclosure Information [Line Items]
Long-term debt	0	0
Medium-term notes	329	322
Investment agreements	331	355
Total liabilities	660	677
Gross	1,214	848
Ceded recoverable (liability)	$ 33	$ 30