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, 2016	Dec. 31, 2015
Investments, Unrealized Loss Position
Less than 12 months fair value	$ 2,079	$ 1,654
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss	71	119
12 months or more fair value	191	284
Available-for-sale Securities, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss	11	37
Total fair value	2,270	1,938
Available-for-sale Securities, Continuous Unrealized Loss Position, Accumulated Loss	82	156
Fixed Maturities
Investments, Unrealized Loss Position
Less than 12 months fair value	1,972	1,349
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss	62	68
12 months or more fair value	191	284
Available-for-sale Securities, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss	11	37
Total fair value	2,163	1,633
Available-for-sale Securities, Continuous Unrealized Loss Position, Accumulated Loss	73	105
Fixed Maturities | Corporate Securities
Investments, Unrealized Loss Position
Less than 12 months fair value	733	1,099
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss	15	63
12 months or more fair value	189	133
Available-for-sale Securities, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss	11	33
Total fair value	922	1,232
Available-for-sale Securities, Continuous Unrealized Loss Position, Accumulated Loss	26	96
Fixed Maturities | States, Municipalities and Political Subdivisions
Investments, Unrealized Loss Position
Less than 12 months fair value	989	47
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss	42	1
12 months or more fair value	0	22
Available-for-sale Securities, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss	0	0
Total fair value	989	69
Available-for-sale Securities, Continuous Unrealized Loss Position, Accumulated Loss	42	1
Fixed Maturities | Commercial Mortgage Backed Securities
Investments, Unrealized Loss Position
Less than 12 months fair value	89	103
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss	2	2
12 months or more fair value	2	2
Available-for-sale Securities, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss	0	0
Total fair value	91	105
Available-for-sale Securities, Continuous Unrealized Loss Position, Accumulated Loss	2	2
Fixed Maturities | Government-Sponsored Enterprises
Investments, Unrealized Loss Position
Less than 12 months fair value	155	100
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss	3	2
12 months or more fair value	0	127
Available-for-sale Securities, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss	0	4
Total fair value	155	227
Available-for-sale Securities, Continuous Unrealized Loss Position, Accumulated Loss	3	6
Fixed Maturities | United States Government
Investments, Unrealized Loss Position
Less than 12 months fair value	6
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	6
Available-for-sale Securities, Continuous Unrealized Loss Position, Accumulated Loss	0
Equity Securities
Investments, Unrealized Loss Position
Less than 12 months fair value	107	305
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss	9	51
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	107	305
Available-for-sale Securities, Continuous Unrealized Loss Position, Accumulated Loss	9	51
Equity Securities | Common Equities
Investments, Unrealized Loss Position
Less than 12 months fair value	103	270
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss	9	51
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	103	270
Available-for-sale Securities, Continuous Unrealized Loss Position, Accumulated Loss	9	51
Equity Securities | Nonredeemable Preferred Equities
Investments, Unrealized Loss Position
Less than 12 months fair value	4	35
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss	0	0
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	4	35
Available-for-sale Securities, Continuous Unrealized Loss Position, Accumulated Loss	$ 0	$ 0