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	Dec. 31, 2020	Dec. 31, 2019
Schedule of Held-to-maturity Securities [Line Items]
Debt Securities, Held-to-maturity	$ 11,697	$ 12,581
Debt Securities, Held-to-maturity, Allowance for Credit Loss	44	0
Debt securities, held to maturity, net carrying value	11,653
Debt Securities, Held-to-maturity, Accumulated Unrecognized Gain	859	427
Debt Securities, Held-to-maturity, Accumulated Unrecognized Loss	(2)	(3)
Held to maturity, Fair Value	12,510	13,005
Held to maturity, OTTI recognized in AOCI		0
U.S. Treasury and agency
Schedule of Held-to-maturity Securities [Line Items]
Debt Securities, Held-to-maturity	1,392	1,318
Debt Securities, Held-to-maturity, Allowance for Credit Loss	0
Debt securities, held to maturity, net carrying value	1,392
Debt Securities, Held-to-maturity, Accumulated Unrecognized Gain	60	29
Debt Securities, Held-to-maturity, Accumulated Unrecognized Loss	0	0
Held to maturity, Fair Value	1,452	1,347
Held to maturity, OTTI recognized in AOCI		0
Foreign
Schedule of Held-to-maturity Securities [Line Items]
Debt Securities, Held-to-maturity	1,295	1,423
Debt Securities, Held-to-maturity, Allowance for Credit Loss	(7)
Debt securities, held to maturity, net carrying value	1,288
Debt Securities, Held-to-maturity, Accumulated Unrecognized Gain	118	62
Debt Securities, Held-to-maturity, Accumulated Unrecognized Loss	(1)	0
Held to maturity, Fair Value	1,405	1,485
Held to maturity, OTTI recognized in AOCI		0
Corporate securities
Schedule of Held-to-maturity Securities [Line Items]
Debt Securities, Held-to-maturity	2,185	2,349
Debt Securities, Held-to-maturity, Allowance for Credit Loss	(35)
Debt securities, held to maturity, net carrying value	2,150
Debt Securities, Held-to-maturity, Accumulated Unrecognized Gain	288	121
Debt Securities, Held-to-maturity, Accumulated Unrecognized Loss	0	(2)
Held to maturity, Fair Value	2,438	2,468
Held to maturity, OTTI recognized in AOCI		0
Mortgage-backed securities
Schedule of Held-to-maturity Securities [Line Items]
Debt Securities, Held-to-maturity	2,000	2,331
Debt Securities, Held-to-maturity, Allowance for Credit Loss	(1)
Debt securities, held to maturity, net carrying value	1,999
Debt Securities, Held-to-maturity, Accumulated Unrecognized Gain	148	65
Debt Securities, Held-to-maturity, Accumulated Unrecognized Loss	(1)	0
Held to maturity, Fair Value	2,146	2,396
Held to maturity, OTTI recognized in AOCI		0
States, municipalities, and political subdivisions
Schedule of Held-to-maturity Securities [Line Items]
Debt Securities, Held-to-maturity	4,825	5,160
Debt Securities, Held-to-maturity, Allowance for Credit Loss	(1)
Debt securities, held to maturity, net carrying value	4,824
Debt Securities, Held-to-maturity, Accumulated Unrecognized Gain	245	150
Debt Securities, Held-to-maturity, Accumulated Unrecognized Loss	0	(1)
Held to maturity, Fair Value	$ 5,069	5,309
Held to maturity, OTTI recognized in AOCI		$ 0