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, 2018	Dec. 31, 2017
Schedule of Held-to-maturity Securities [Line Items]
Debt Securities, Held-to-maturity	$ 13,435	$ 14,335
Debt Securities, Held-to-maturity, Accumulated Unrecognized Gain	51	179
Debt Securities, Held-to-maturity, Accumulated Unrecognized Loss	(227)	(40)
Held to maturity, Fair Value	13,259	14,474
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	1,185	908
Debt Securities, Held-to-maturity, Accumulated Unrecognized Gain	8	12
Debt Securities, Held-to-maturity, Accumulated Unrecognized Loss	(11)	(5)
Held to maturity, Fair Value	1,182	915
Held to maturity, OTTI recognized in AOCI	0	0
Foreign
Schedule of Held-to-maturity Securities [Line Items]
Debt Securities, Held-to-maturity	1,549	1,738
Debt Securities, Held-to-maturity, Accumulated Unrecognized Gain	11	27
Debt Securities, Held-to-maturity, Accumulated Unrecognized Loss	(18)	(8)
Held to maturity, Fair Value	1,542	1,757
Held to maturity, OTTI recognized in AOCI	0	0
Corporate securities
Schedule of Held-to-maturity Securities [Line Items]
Debt Securities, Held-to-maturity	2,601	3,159
Debt Securities, Held-to-maturity, Accumulated Unrecognized Gain	11	67
Debt Securities, Held-to-maturity, Accumulated Unrecognized Loss	(104)	(7)
Held to maturity, Fair Value	2,508	3,219
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	2,524	2,724
Debt Securities, Held-to-maturity, Accumulated Unrecognized Gain	5	23
Debt Securities, Held-to-maturity, Accumulated Unrecognized Loss	(43)	(5)
Held to maturity, Fair Value	2,486	2,742
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	5,576	5,806
Debt Securities, Held-to-maturity, Accumulated Unrecognized Gain	16	50
Debt Securities, Held-to-maturity, Accumulated Unrecognized Loss	(51)	(15)
Held to maturity, Fair Value	5,541	5,841
Held to maturity, OTTI recognized in AOCI	$ 0	$ 0