Investments (Fixed Maturity and Equity Securities Available-For-Sale by Sector) (Details) - USD ($) $ in Millions	Sep. 30, 2016	Dec. 31, 2015	Dec. 31, 2014
Available-for-sale Securities [Abstract]
Cost or Amortized Cost	$ 353,913	$ 332,964
Cost or Amortized Cost	2,838	2,997
Gross Unrealized OTTI Loss	(13)	(76)	$ (112)
Available-for-sale Securities, Debt Securities	390,442	351,402
Equity securities	3,289	3,321
Fixed Maturity Securities
Available-for-sale Securities [Abstract]
Cost or Amortized Cost	353,913	332,964
Gross Unrealized Gain	39,334	23,883
Gross Unrealized Temporary Loss	2,792	5,369
Gross Unrealized OTTI Loss	13	76
Available-for-sale Securities, Debt Securities	390,442	351,402
U.S. corporate
Available-for-sale Securities [Abstract]
Cost or Amortized Cost	95,808	96,466
Gross Unrealized Gain	10,589	6,583
Gross Unrealized Temporary Loss	721	2,255
Gross Unrealized OTTI Loss	0	0
Available-for-sale Securities, Debt Securities	105,676	100,794
U.S. government and agency
Available-for-sale Securities [Abstract]
Cost or Amortized Cost	60,340	56,499
Gross Unrealized Gain	9,491	5,373
Gross Unrealized Temporary Loss	46	226
Gross Unrealized OTTI Loss	0	0
Available-for-sale Securities, Debt Securities	69,785	61,646
Foreign corporate
Available-for-sale Securities [Abstract]
Cost or Amortized Cost	57,423	56,003
Gross Unrealized Gain	4,264	3,019
Gross Unrealized Temporary Loss	1,268	1,822
Gross Unrealized OTTI Loss	0	2
Available-for-sale Securities, Debt Securities	60,419	57,198
Foreign government
Available-for-sale Securities [Abstract]
Cost or Amortized Cost	54,425	45,451
Gross Unrealized Gain	9,479	5,269
Gross Unrealized Temporary Loss	139	221
Gross Unrealized OTTI Loss	0	0
Available-for-sale Securities, Debt Securities	63,765	50,499
RMBS
Available-for-sale Securities [Abstract]
Cost or Amortized Cost	43,838	37,914
Gross Unrealized Gain	1,788	1,366
Gross Unrealized Temporary Loss	310	424
Gross Unrealized OTTI Loss	7	59
Available-for-sale Securities, Debt Securities	45,309	38,797
State and political subdivision
Available-for-sale Securities [Abstract]
Cost or Amortized Cost	14,539	13,723
Gross Unrealized Gain	2,939	1,795
Gross Unrealized Temporary Loss	11	67
Gross Unrealized OTTI Loss	4	10
Available-for-sale Securities, Debt Securities	17,463	15,441
ABS
Available-for-sale Securities [Abstract]
Cost or Amortized Cost	15,685	14,498
Gross Unrealized Gain	122	131
Gross Unrealized Temporary Loss	220	229
Gross Unrealized OTTI Loss	3	6
Available-for-sale Securities, Debt Securities	15,584	14,394
CMBS (1)
Available-for-sale Securities [Abstract]
Cost or Amortized Cost	11,855	12,410
Gross Unrealized Gain	662	347
Gross Unrealized Temporary Loss	77	125
Gross Unrealized OTTI Loss	(1)	(1)
Available-for-sale Securities, Debt Securities	12,441	12,633
Equity securities
Available-for-sale Securities [Abstract]
Cost or Amortized Cost	2,838	2,997
Gross Unrealized Gain	512	482
Gross Unrealized Temporary Loss	61	158
Gross Unrealized OTTI Loss	0	0
Equity securities	3,289	3,321
Common Stock
Available-for-sale Securities [Abstract]
Cost or Amortized Cost	2,000	1,962
Gross Unrealized Gain	449	397
Gross Unrealized Temporary Loss	14	107
Gross Unrealized OTTI Loss	0	0
Equity securities	2,435	2,252
Non-redeemable preferred stock
Available-for-sale Securities [Abstract]
Cost or Amortized Cost	838	1,035
Gross Unrealized Gain	63	85
Gross Unrealized Temporary Loss	47	51
Gross Unrealized OTTI Loss	0	0
Equity securities	$ 854	$ 1,069