Investments (Fair Values And Unrealized Losses By Investment Category And By The Duration Of The Securities' Continuous Unrealized Loss Position) (Details) - USD ($) $ in Millions	Dec. 31, 2017	Dec. 31, 2016
Investments, Unrealized Loss Position
Less than 12 months fair value	$ 809	$ 2,079
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss	20	71
12 months or more fair value	682	191
Available-for-sale Securities, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss	18	11
Total fair value	1,491	2,270
Available-for-sale Securities, Continuous Unrealized Loss Position, Accumulated Loss	38	82
Fixed Maturities
Investments, Unrealized Loss Position
Less than 12 months fair value	580	1,972
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss	6	62
12 months or more fair value	682	191
Available-for-sale Securities, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss	18	11
Total fair value	1,262	2,163
Available-for-sale Securities, Continuous Unrealized Loss Position, Accumulated Loss	24	73
Fixed Maturities | Corporate Securities
Investments, Unrealized Loss Position
Less than 12 months fair value	330	733
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss	4	15
12 months or more fair value	252	189
Available-for-sale Securities, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss	9	11
Total fair value	582	922
Available-for-sale Securities, Continuous Unrealized Loss Position, Accumulated Loss	13	26
Fixed Maturities | States, Municipalities and Political Subdivisions
Investments, Unrealized Loss Position
Less than 12 months fair value	88	989
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss	1	42
12 months or more fair value	264	0
Available-for-sale Securities, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss	5	0
Total fair value	352	989
Available-for-sale Securities, Continuous Unrealized Loss Position, Accumulated Loss	6	42
Fixed Maturities | Commercial Mortgage Backed Securities
Investments, Unrealized Loss Position
Less than 12 months fair value	33	89
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss	0	2
12 months or more fair value	36	2
Available-for-sale Securities, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss	1	0
Total fair value	69	91
Available-for-sale Securities, Continuous Unrealized Loss Position, Accumulated Loss	1	2
Fixed Maturities | Government-Sponsored Enterprises
Investments, Unrealized Loss Position
Less than 12 months fair value	96	155
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss	1	3
12 months or more fair value	124	0
Available-for-sale Securities, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss	3	0
Total fair value	220	155
Available-for-sale Securities, Continuous Unrealized Loss Position, Accumulated Loss	4	3
Fixed Maturities | Foreign government
Investments, Unrealized Loss Position
Less than 12 months fair value	10
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss	0
12 months or more fair value	0
Available-for-sale Securities, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss	0
Total fair value	10
Available-for-sale Securities, Continuous Unrealized Loss Position, Accumulated Loss	0
Fixed Maturities | United States Government
Investments, Unrealized Loss Position
Less than 12 months fair value	23	6
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss	0	0
12 months or more fair value	6	0
Available-for-sale Securities, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss	0	0
Total fair value	29	6
Available-for-sale Securities, Continuous Unrealized Loss Position, Accumulated Loss	0	0
Equity Securities
Investments, Unrealized Loss Position
Less than 12 months fair value	229	107
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss	14	9
12 months or more fair value	0	0
Available-for-sale Securities, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss	0	0
Total fair value	229	107
Available-for-sale Securities, Continuous Unrealized Loss Position, Accumulated Loss	14	9
Equity Securities | Common Equities
Investments, Unrealized Loss Position
Less than 12 months fair value	229	103
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss	14	9
12 months or more fair value	0	0
Available-for-sale Securities, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss	0	0
Total fair value	229	103
Available-for-sale Securities, Continuous Unrealized Loss Position, Accumulated Loss	$ 14	9
Equity Securities | Nonredeemable Preferred Equities
Investments, Unrealized Loss Position
Less than 12 months fair value		4
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss		0
12 months or more fair value		0
Available-for-sale Securities, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss		0
Total fair value		4
Available-for-sale Securities, Continuous Unrealized Loss Position, Accumulated Loss		$ 0