Investments (Fixed Maturity and Equity Securities Available-For-Sale by Sector) (Details) - USD ($) $ in Millions	Mar. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Available-for-sale Securities [Abstract]
Cost or Amortized Cost	$ 343,412	$ 332,964
Cost or Amortized Cost	3,010	2,997
Gross Unrealized OTTI Loss	(91)	(76)	$ (112)
Fixed maturity securities available-for-sale, at estimated fair value (amortized cost: $343,412 and $332,964, respectively; includes $3,396 and $4,277, respectively, relating to variable interest entities)	371,981	351,402
Equity securities	3,374	3,321
Fixed Maturity Securities
Available-for-sale Securities [Abstract]
Cost or Amortized Cost	343,412	332,964
Gross Unrealized Gain	32,267	23,883
Gross Unrealized Temporary Loss	3,607	5,369
Gross Unrealized OTTI Loss	91	76
Fixed maturity securities available-for-sale, at estimated fair value (amortized cost: $343,412 and $332,964, respectively; includes $3,396 and $4,277, respectively, relating to variable interest entities)	371,981	351,402
U.S. corporate
Available-for-sale Securities [Abstract]
Cost or Amortized Cost	95,066	96,466
Gross Unrealized Gain	8,350	6,583
Gross Unrealized Temporary Loss	1,320	2,255
Gross Unrealized OTTI Loss	0	0
Fixed maturity securities available-for-sale, at estimated fair value (amortized cost: $343,412 and $332,964, respectively; includes $3,396 and $4,277, respectively, relating to variable interest entities)	102,096	100,794
U.S. government and agency
Available-for-sale Securities [Abstract]
Cost or Amortized Cost	57,060	56,499
Gross Unrealized Gain	7,969	5,373
Gross Unrealized Temporary Loss	38	226
Gross Unrealized OTTI Loss	0	0
Fixed maturity securities available-for-sale, at estimated fair value (amortized cost: $343,412 and $332,964, respectively; includes $3,396 and $4,277, respectively, relating to variable interest entities)	64,991	61,646
Foreign corporate
Available-for-sale Securities [Abstract]
Cost or Amortized Cost	56,756	56,003
Gross Unrealized Gain	3,612	3,019
Gross Unrealized Temporary Loss	1,273	1,822
Gross Unrealized OTTI Loss	4	2
Fixed maturity securities available-for-sale, at estimated fair value (amortized cost: $343,412 and $332,964, respectively; includes $3,396 and $4,277, respectively, relating to variable interest entities)	59,091	57,198
Foreign government
Available-for-sale Securities [Abstract]
Cost or Amortized Cost	48,940	45,451
Gross Unrealized Gain	7,848	5,269
Gross Unrealized Temporary Loss	132	221
Gross Unrealized OTTI Loss	0	0
Fixed maturity securities available-for-sale, at estimated fair value (amortized cost: $343,412 and $332,964, respectively; includes $3,396 and $4,277, respectively, relating to variable interest entities)	56,656	50,499
RMBS
Available-for-sale Securities [Abstract]
Cost or Amortized Cost	41,940	37,914
Gross Unrealized Gain	1,577	1,366
Gross Unrealized Temporary Loss	414	424
Gross Unrealized OTTI Loss	74	59
Fixed maturity securities available-for-sale, at estimated fair value (amortized cost: $343,412 and $332,964, respectively; includes $3,396 and $4,277, respectively, relating to variable interest entities)	43,029	38,797
State and political subdivision
Available-for-sale Securities [Abstract]
Cost or Amortized Cost	14,243	13,723
Gross Unrealized Gain	2,320	1,795
Gross Unrealized Temporary Loss	16	67
Gross Unrealized OTTI Loss	8	10
Fixed maturity securities available-for-sale, at estimated fair value (amortized cost: $343,412 and $332,964, respectively; includes $3,396 and $4,277, respectively, relating to variable interest entities)	16,539	15,441
ABS
Available-for-sale Securities [Abstract]
Cost or Amortized Cost	16,407	14,498
Gross Unrealized Gain	121	131
Gross Unrealized Temporary Loss	320	229
Gross Unrealized OTTI Loss	6	6
Fixed maturity securities available-for-sale, at estimated fair value (amortized cost: $343,412 and $332,964, respectively; includes $3,396 and $4,277, respectively, relating to variable interest entities)	16,202	14,394
CMBS (1)
Available-for-sale Securities [Abstract]
Cost or Amortized Cost	13,000	12,410
Gross Unrealized Gain	470	347
Gross Unrealized Temporary Loss	94	125
Gross Unrealized OTTI Loss	(1)	(1)
Fixed maturity securities available-for-sale, at estimated fair value (amortized cost: $343,412 and $332,964, respectively; includes $3,396 and $4,277, respectively, relating to variable interest entities)	13,377	12,633
Equity securities
Available-for-sale Securities [Abstract]
Cost or Amortized Cost	3,010	2,997
Gross Unrealized Gain	481	482
Gross Unrealized Temporary Loss	117	158
Gross Unrealized OTTI Loss	0	0
Equity securities	3,374	3,321
Common Stock
Available-for-sale Securities [Abstract]
Cost or Amortized Cost	2,051	1,962
Gross Unrealized Gain	412	397
Gross Unrealized Temporary Loss	48	107
Gross Unrealized OTTI Loss	0	0
Equity securities	2,415	2,252
Non-redeemable preferred stock
Available-for-sale Securities [Abstract]
Cost or Amortized Cost	959	1,035
Gross Unrealized Gain	69	85
Gross Unrealized Temporary Loss	69	51
Gross Unrealized OTTI Loss	0	0
Equity securities	$ 959	$ 1,069