Derivative Financial Instruments and Off-balance sheet Financial Instruments (Details) $ in Millions	12 Months Ended
	Dec. 31, 2015 USD ($) contract shares	Dec. 31, 2014 USD ($) contract shares
Derivative Financial Instruments and Off-balance sheet Financial Instruments
Assumed recoveries under sale of credit protection	$ 0
Cash and securities pledged in the form of margin deposits	20
Derivatives, Fair Value
Total asset derivatives, Notional amount	1,568	$ 1,851
Total liability derivatives, Notional amount	3,409	3,910
Total derivatives, Notional amount	$ 4,977	$ 5,761
Total asset derivatives, Number of contracts | contract	5,627	5,429
Total liability derivatives, Number of contracts | contract	4,406	4,660
Total derivatives, Number of contracts | contract	10,033	10,089
Net amount on balance sheet	$ 61	$ 78
Asset derivatives, Gross asset	63	94
Asset derivatives, Gross liability	(2)	(16)
Net amount on balance sheet	(323)	(361)
Total derivatives, Fair value, net	(262)	(283)
Liability derivatives, Gross asset	6	6
Liability derivatives, Gross liability	$ (329)	$ (367)
Number of stock rights and warrants held by the company related to derivative contracts (in shares) | shares	220	220
Derivatives not designated as accounting hedging instruments
Derivatives, Fair Value
Total asset derivatives, Notional amount	$ 1,523	$ 1,766
Total liability derivatives, Notional amount	$ 3,390	$ 3,860
Total asset derivatives, Number of contracts | contract	5,627	5,429
Total liability derivatives, Number of contracts | contract	4,406	4,660
Net amount on balance sheet	$ 55	$ 75
Asset derivatives, Gross asset	57	91
Asset derivatives, Gross liability	(2)	(16)
Net amount on balance sheet	(327)	(360)
Liability derivatives, Gross asset	2	6
Liability derivatives, Gross liability	(329)	(366)
Other liabilities & accrued expenses | Derivatives not designated as accounting hedging instruments
Derivatives, Fair Value
Total liability derivatives, Notional amount		$ 0
Total liability derivatives, Number of contracts | contract		700
Net amount on balance sheet		$ 0
Liability derivatives, Gross asset		0
Liability derivatives, Gross liability		0
Foreign currency swap agreements | Other investments | Derivatives designated as accounting hedging instruments
Derivatives, Fair Value
Total asset derivatives, Notional amount	45	85
Net amount on balance sheet	6	3
Asset derivatives, Gross asset	6	3
Asset derivatives, Gross liability	0	0
Foreign currency swap agreements | Other liabilities & accrued expenses | Derivatives designated as accounting hedging instruments
Derivatives, Fair Value
Total liability derivatives, Notional amount	19	50
Net amount on balance sheet	4	(1)
Liability derivatives, Gross asset	4	0
Liability derivatives, Gross liability	0	(1)
Interest rate swap agreements | Other liabilities & accrued expenses | Derivatives not designated as accounting hedging instruments
Derivatives, Fair Value
Total liability derivatives, Notional amount	85	85
Net amount on balance sheet	0	1
Liability derivatives, Gross asset	0	1
Liability derivatives, Gross liability	0	0
Interest rate cap agreements | Other investments | Derivatives not designated as accounting hedging instruments
Derivatives, Fair Value
Total asset derivatives, Notional amount	42	163
Net amount on balance sheet	0	2
Asset derivatives, Gross asset	0	2
Asset derivatives, Gross liability	0	0
Interest rate cap agreements | Other liabilities & accrued expenses | Derivatives not designated as accounting hedging instruments
Derivatives, Fair Value
Total liability derivatives, Notional amount	72	11
Net amount on balance sheet	1	0
Liability derivatives, Gross asset	1	0
Liability derivatives, Gross liability	0	0
Options | Other liabilities & accrued expenses | Derivatives not designated as accounting hedging instruments
Derivatives, Fair Value
Total liability derivatives, Notional amount		$ 0
Total liability derivatives, Number of contracts | contract		3,960
Net amount on balance sheet		$ (23)
Liability derivatives, Gross asset		0
Liability derivatives, Gross liability		(23)
Options and futures | Other liabilities & accrued expenses | Derivatives not designated as accounting hedging instruments
Derivatives, Fair Value
Total liability derivatives, Notional amount	$ 0
Total liability derivatives, Number of contracts | contract	4,406
Net amount on balance sheet	$ (7)
Liability derivatives, Gross asset	0
Liability derivatives, Gross liability	(7)
Options and warrants | Other investments | Derivatives not designated as accounting hedging instruments
Derivatives, Fair Value
Total asset derivatives, Notional amount	$ 0	$ 0
Total asset derivatives, Number of contracts | contract	3,730	3,225
Net amount on balance sheet	$ 44	$ 83
Asset derivatives, Gross asset	44	83
Asset derivatives, Gross liability	0	0
Financial futures contracts | Other assets | Derivatives not designated as accounting hedging instruments
Derivatives, Fair Value
Total asset derivatives, Notional amount	$ 0	$ 0
Total asset derivatives, Number of contracts | contract	1,897	2,204
Net amount on balance sheet	$ 2	$ 2
Asset derivatives, Gross asset	2	2
Asset derivatives, Gross liability	0	0
Foreign currency forwards | Other investments | Derivatives not designated as accounting hedging instruments
Derivatives, Fair Value
Total asset derivatives, Notional amount	185	471
Net amount on balance sheet	1	(15)
Asset derivatives, Gross asset	2	1
Asset derivatives, Gross liability	(1)	(16)
Foreign currency forwards | Other liabilities & accrued expenses | Derivatives not designated as accounting hedging instruments
Derivatives, Fair Value
Total liability derivatives, Notional amount	361	228
Net amount on balance sheet	(12)	(1)
Liability derivatives, Gross asset	1	2
Liability derivatives, Gross liability	(13)	(3)
Guaranteed accumulation benefits | Contractholder funds | Derivatives not designated as accounting hedging instruments
Derivatives, Fair Value
Total liability derivatives, Notional amount	481	615
Net amount on balance sheet	(38)	(32)
Liability derivatives, Gross asset	0	0
Liability derivatives, Gross liability	(38)	(32)
Guaranteed withdrawal benefits | Contractholder funds | Derivatives not designated as accounting hedging instruments
Derivatives, Fair Value
Total liability derivatives, Notional amount	332	425
Net amount on balance sheet	(14)	(13)
Liability derivatives, Gross asset	0	0
Liability derivatives, Gross liability	(14)	(13)
Equity-indexed and forward starting options in life and annuity product contracts | Contractholder funds | Derivatives not designated as accounting hedging instruments
Derivatives, Fair Value
Total liability derivatives, Notional amount	1,781	1,786
Net amount on balance sheet	(247)	(278)
Liability derivatives, Gross asset	0	0
Liability derivatives, Gross liability	(247)	(278)
Other embedded derivative financial instruments | Other investments | Derivatives not designated as accounting hedging instruments
Derivatives, Fair Value
Total asset derivatives, Notional amount	1,000	1,000
Net amount on balance sheet	0	0
Asset derivatives, Gross asset	0	0
Asset derivatives, Gross liability	0	0
Other embedded derivative financial instruments | Contractholder funds | Derivatives not designated as accounting hedging instruments
Derivatives, Fair Value
Total liability derivatives, Notional amount	85	85
Net amount on balance sheet	0	0
Liability derivatives, Gross asset	0	0
Liability derivatives, Gross liability	0	0
Credit default swaps — buying protection | Other investments | Derivatives not designated as accounting hedging instruments
Derivatives, Fair Value
Total asset derivatives, Notional amount	112	29
Net amount on balance sheet	4	0
Asset derivatives, Gross asset	5	0
Asset derivatives, Gross liability	(1)	0
Credit default swaps — buying protection | Other liabilities & accrued expenses | Derivatives not designated as accounting hedging instruments
Derivatives, Fair Value
Total liability derivatives, Notional amount	88	420
Net amount on balance sheet	(2)	(6)
Liability derivatives, Gross asset	0	1
Liability derivatives, Gross liability	(2)	(7)
Credit default swaps — selling protection | Other investments | Derivatives not designated as accounting hedging instruments
Derivatives, Fair Value
Total asset derivatives, Notional amount	150	100
Net amount on balance sheet	2	2
Asset derivatives, Gross asset	2	2
Asset derivatives, Gross liability	0	0
Credit default swaps — selling protection | Other liabilities & accrued expenses | Derivatives not designated as accounting hedging instruments
Derivatives, Fair Value
Total liability derivatives, Notional amount	105	205
Net amount on balance sheet	(8)	(8)
Liability derivatives, Gross asset	0	2
Liability derivatives, Gross liability	(8)	(10)
Other contracts | Other investments | Derivatives not designated as accounting hedging instruments
Derivatives, Fair Value
Total asset derivatives, Notional amount	31
Net amount on balance sheet	1
Asset derivatives, Gross asset	1
Asset derivatives, Gross liability	0
Other contracts | Other assets | Derivatives not designated as accounting hedging instruments
Derivatives, Fair Value
Total asset derivatives, Notional amount	3	3
Net amount on balance sheet	1	1
Asset derivatives, Gross asset	1	1
Asset derivatives, Gross liability	$ 0	$ 0