Investments (Schedule Of Amortized Cost And Fair Value Of Held-to-Maturity And Related Other-Than-Temporary Impairment Recognized In Accumulated Other Comprehensive Income) (Detail) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018
Schedule of Held-to-maturity Securities [Line Items]
Document Period End Date	Dec. 31, 2019
Debt Securities, Held-to-maturity	$ 12,581	$ 13,435
Debt Securities, Held-to-maturity, Accumulated Unrecognized Gain	427	51
Debt Securities, Held-to-maturity, Accumulated Unrecognized Loss	(3)	(227)
Held to maturity, Fair Value	13,005	13,259
Held to maturity, OTTI recognized in AOCI	0	0
U.S. Treasury and agency
Schedule of Held-to-maturity Securities [Line Items]
Debt Securities, Held-to-maturity	1,318	1,185
Debt Securities, Held-to-maturity, Accumulated Unrecognized Gain	29	8
Debt Securities, Held-to-maturity, Accumulated Unrecognized Loss	0	(11)
Held to maturity, Fair Value	1,347	1,182
Held to maturity, OTTI recognized in AOCI	0	0
Foreign
Schedule of Held-to-maturity Securities [Line Items]
Debt Securities, Held-to-maturity	1,423	1,549
Debt Securities, Held-to-maturity, Accumulated Unrecognized Gain	62	11
Debt Securities, Held-to-maturity, Accumulated Unrecognized Loss	0	(18)
Held to maturity, Fair Value	1,485	1,542
Held to maturity, OTTI recognized in AOCI	0	0
Corporate securities
Schedule of Held-to-maturity Securities [Line Items]
Debt Securities, Held-to-maturity	2,349	2,601
Debt Securities, Held-to-maturity, Accumulated Unrecognized Gain	121	11
Debt Securities, Held-to-maturity, Accumulated Unrecognized Loss	(2)	(104)
Held to maturity, Fair Value	2,468	2,508
Held to maturity, OTTI recognized in AOCI	0	0
Mortgage-backed securities
Schedule of Held-to-maturity Securities [Line Items]
Debt Securities, Held-to-maturity	2,331	2,524
Debt Securities, Held-to-maturity, Accumulated Unrecognized Gain	65	5
Debt Securities, Held-to-maturity, Accumulated Unrecognized Loss	0	(43)
Held to maturity, Fair Value	2,396	2,486
Held to maturity, OTTI recognized in AOCI	0	0
States, municipalities, and political subdivisions
Schedule of Held-to-maturity Securities [Line Items]
Debt Securities, Held-to-maturity	5,160	5,576
Debt Securities, Held-to-maturity, Accumulated Unrecognized Gain	150	16
Debt Securities, Held-to-maturity, Accumulated Unrecognized Loss	(1)	(51)
Held to maturity, Fair Value	5,309	5,541
Held to maturity, OTTI recognized in AOCI	$ 0	$ 0