Reserve for Life-Contingent Contract Benefits and Contractholder Funds (Details 4) (Variable annuities, USD $)	12 Months Ended
	Dec. 31, 2014	Dec. 31, 2013
Variable annuity contracts with guarantees
Account balances of separate accounts with guarantees, invested in equity, fixed income and balanced mutual funds	$ 3,820,000,000	$ 5,200,000,000
Account balances of separate accounts with guarantees, invested in money market mutual funds	467,000,000	748,000,000
In the event of death
Variable annuity contracts with guarantees
Separate account value in the event of death	4,288,000,000	5,951,000,000
Net amount at risk in the event of death	581,000,000	636,000,000
Average attained age of contractholders	69 years	68 years
Liability for guarantees related to income benefits
Variable annuity contracts with guarantees
Separate account value at annuitization	1,142,000,000	1,463,000,000
Net amount at risk at annuitization	238,000,000	252,000,000
Weighted average waiting period until annuitization or guarantee date	0 years	0 years
For cumulative periodic withdrawals
Variable annuity contracts with guarantees
Separate account value	382,000,000	488,000,000
Net amount at risk	8,000,000	9,000,000
Accumulation at specified dates
Variable annuity contracts with guarantees
Separate account value	480,000,000	732,000,000
Net amount at risk	$ 24,000,000	$ 27,000,000
Weighted average waiting period until annuitization or guarantee date	4 years	5 years