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, 2016	Dec. 31, 2015
Schedule of Held-to-maturity Securities [Line Items]
Held to maturity, Amortized Cost	$ 10,644	$ 8,430
Held-to-maturity Securities, Accumulated Unrecognized Holding Gain	148	190
Held-to-maturity Securities, Accumulated Unrecognized Holding Loss	(122)	(68)
Held to maturity, Fair Value	10,670	8,552
Held to maturity, OTTI recognized in AOCI		0
U.S. Treasury and agency
Schedule of Held-to-maturity Securities [Line Items]
Held to maturity, Amortized Cost	655	733
Held-to-maturity Securities, Accumulated Unrecognized Holding Gain	9	13
Held-to-maturity Securities, Accumulated Unrecognized Holding Loss	(3)	(1)
Held to maturity, Fair Value	661	745
Held to maturity, OTTI recognized in AOCI	0	0
Foreign
Schedule of Held-to-maturity Securities [Line Items]
Held to maturity, Amortized Cost	640	763
Held-to-maturity Securities, Accumulated Unrecognized Holding Gain	28	30
Held-to-maturity Securities, Accumulated Unrecognized Holding Loss	(1)	(8)
Held to maturity, Fair Value	667	785
Held to maturity, OTTI recognized in AOCI	0	0
Corporate securities
Schedule of Held-to-maturity Securities [Line Items]
Held to maturity, Amortized Cost	2,771	3,054
Held-to-maturity Securities, Accumulated Unrecognized Holding Gain	50	57
Held-to-maturity Securities, Accumulated Unrecognized Holding Loss	(26)	(55)
Held to maturity, Fair Value	2,795	3,056
Held to maturity, OTTI recognized in AOCI	0	0
Mortgage backed-securities
Schedule of Held-to-maturity Securities [Line Items]
Held to maturity, Amortized Cost	1,393	1,707
Held-to-maturity Securities, Accumulated Unrecognized Holding Gain	35	38
Held-to-maturity Securities, Accumulated Unrecognized Holding Loss	0	(2)
Held to maturity, Fair Value	1,428	1,743
Held to maturity, OTTI recognized in AOCI	0	0
States, municipalities, and political subdivisions
Schedule of Held-to-maturity Securities [Line Items]
Held to maturity, Amortized Cost	5,185	2,173
Held-to-maturity Securities, Accumulated Unrecognized Holding Gain	26	52
Held-to-maturity Securities, Accumulated Unrecognized Holding Loss	(92)	(2)
Held to maturity, Fair Value	5,119	2,223
Held to maturity, OTTI recognized in AOCI	$ 0	$ 0