Derivative Financial Instruments and Off-balance sheet Financial Instruments (Details) $ in Millions	12 Months Ended
	Dec. 31, 2016 USD ($) contract	Dec. 31, 2015 USD ($) 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	9
Derivatives, Fair Value
Total asset derivatives, Notional amount	1,103	$ 1,568
Total liability derivatives, Notional amount	2,673	3,409
Total derivatives, Notional amount	$ 3,776	$ 4,977
Total asset derivatives, Number of contracts | contract	4,233	5,627
Total liability derivatives, Number of contracts | contract	4,848	4,406
Total derivatives, Number of contracts | contract	9,081	10,033
Net amount on balance sheet	$ 93	$ 61
Asset derivatives, Gross asset	121	63
Asset derivatives, gross liability	(28)	(2)
Net amount on balance sheet	(334)	(323)
Total derivatives, Fair value, net	(241)	(262)
Liability derivatives, Gross asset	0	6
Liability derivatives, Gross liability	(334)	$ (329)
Number of stock rights and warrants held by the company related to derivative contracts (in shares) | shares		220
Derivatives not designated as accounting hedging instruments
Derivatives, Fair Value
Total asset derivatives, Notional amount	1,054	$ 1,523
Total liability derivatives, Notional amount	$ 2,673	$ 3,390
Total asset derivatives, Number of contracts | contract	4,233	5,627
Total liability derivatives, Number of contracts | contract	4,848	4,406
Net amount on balance sheet	$ 88	$ 55
Asset derivatives, Gross asset	116	57
Asset derivatives, gross liability	(28)	(2)
Net amount on balance sheet	(334)	(327)
Liability derivatives, Gross asset	0	2
Liability derivatives, Gross liability	(334)	(329)
Foreign currency swap agreements | Other investments | Derivatives designated as accounting hedging instruments
Derivatives, Fair Value
Total asset derivatives, Notional amount	49	45
Net amount on balance sheet	5	6
Asset derivatives, Gross asset	5	6
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
Net amount on balance sheet		4
Liability derivatives, Gross asset		4
Liability derivatives, Gross liability		0
Interest rate swap agreements | Other liabilities & accrued expenses | Derivatives not designated as accounting hedging instruments
Derivatives, Fair Value
Total liability derivatives, Notional amount		85
Net amount on balance sheet		0
Liability derivatives, Gross asset		0
Liability derivatives, Gross liability		0
Interest rate cap agreements | Other investments | Derivatives not designated as accounting hedging instruments
Derivatives, Fair Value
Total asset derivatives, Notional amount	65	42
Net amount on balance sheet	1	0
Asset derivatives, Gross asset	1	0
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
Net amount on balance sheet		1
Liability derivatives, Gross asset		1
Liability derivatives, Gross liability		0
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	3,972	3,730
Net amount on balance sheet	$ 88	$ 44
Asset derivatives, Gross asset	88	44
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	261	1,897
Net amount on balance sheet	$ 0	$ 2
Asset derivatives, Gross asset	0	2
Asset derivatives, gross liability	0	0
Options and futures | Other liabilities & accrued expenses | Derivatives not designated as accounting hedging instruments
Derivatives, Fair Value
Total liability derivatives, Notional amount	$ 0	$ 0
Total liability derivatives, Number of contracts | contract	4,848	4,406
Net amount on balance sheet	$ (39)	$ (7)
Liability derivatives, Gross asset	0	0
Liability derivatives, Gross liability	(39)	(7)
Foreign currency forwards | Other investments | Derivatives not designated as accounting hedging instruments
Derivatives, Fair Value
Total asset derivatives, Notional amount	759	185
Net amount on balance sheet	0	1
Asset derivatives, Gross asset	24	2
Asset derivatives, gross liability	(24)	(1)
Foreign currency forwards | Other liabilities & accrued expenses | Derivatives not designated as accounting hedging instruments
Derivatives, Fair Value
Total liability derivatives, Notional amount		361
Net amount on balance sheet		(12)
Liability derivatives, Gross asset		1
Liability derivatives, Gross liability		(13)
Guaranteed accumulation benefits | Contractholder funds | Derivatives not designated as accounting hedging instruments
Derivatives, Fair Value
Total liability derivatives, Notional amount	391	481
Net amount on balance sheet	(34)	(38)
Liability derivatives, Gross asset	0	0
Liability derivatives, Gross liability	(34)	(38)
Guaranteed withdrawal benefits | Contractholder funds | Derivatives not designated as accounting hedging instruments
Derivatives, Fair Value
Total liability derivatives, Notional amount	290	332
Net amount on balance sheet	(9)	(14)
Liability derivatives, Gross asset	0	0
Liability derivatives, Gross liability	(9)	(14)
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	1,751	1,781
Net amount on balance sheet	(247)	(247)
Liability derivatives, Gross asset	0	0
Liability derivatives, Gross liability	(247)	(247)
Other embedded derivative financial instruments | Other investments | Derivatives not designated as accounting hedging instruments
Derivatives, Fair Value
Total asset derivatives, Notional amount		1,000
Net amount on balance sheet		0
Asset derivatives, Gross asset		0
Asset derivatives, gross liability		0
Other embedded derivative financial instruments | Contractholder funds | Derivatives not designated as accounting hedging instruments
Derivatives, Fair Value
Total liability derivatives, Notional amount		85
Net amount on balance sheet		0
Liability derivatives, Gross asset		0
Liability derivatives, Gross liability		0
Credit default swaps – buying protection | Other investments | Derivatives not designated as accounting hedging instruments
Derivatives, Fair Value
Total asset derivatives, Notional amount	87	112
Net amount on balance sheet	(4)	4
Asset derivatives, Gross asset	0	5
Asset derivatives, gross liability	(4)	(1)
Credit default swaps – buying protection | Other liabilities & accrued expenses | Derivatives not designated as accounting hedging instruments
Derivatives, Fair Value
Total liability derivatives, Notional amount	136	88
Net amount on balance sheet	(2)	(2)
Liability derivatives, Gross asset	0	0
Liability derivatives, Gross liability	(2)	(2)
Credit default swaps – selling protection | Other investments | Derivatives not designated as accounting hedging instruments
Derivatives, Fair Value
Total asset derivatives, Notional amount	140	150
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	105
Net amount on balance sheet	(3)	(8)
Liability derivatives, Gross asset	0	0
Liability derivatives, Gross liability	(3)	(8)
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