Fair Value Measurements - Assets and Liabilities by Level (Details) (USD $) In Millions, unless otherwise specified	3 Months Ended		12 Months Ended
	Mar. 31, 2013		Dec. 31, 2012
Fixed maturities:
Total fixed maturities	$ 16,600		$ 17,705
Equity securities	131		111
Short-term investments	122		154
Financial liabilities at fair value:
Percentage of GMIB exposure covered by retrocessional coverage			55.00%
Unrealized Appreciation Settlement Annuity	810		875
Fair Value, Measurements, Recurring [Member]
Fixed maturities:
Federal government and agency	847		902
State and local government	2,401		2,437
Foreign government	1,242		1,322
Corporate	11,006		11,896
Federal agency mortgage-backed	107		122
Other mortgage-backed	83		89
Other asset-backed	914		937
Total fixed maturities	16,600	[1]	17,705	[2]
Equity securities	131		111
Subtotal	16,731		17,816
Short-term investments	122		154
GMIB assets	1,117	[3]	622	[4]
Other derivative assets	7	[5]	41	[6]
Total financial assets at fair value, excluding separate accounts	17,977		18,633
Financial liabilities at fair value:
GMIB liabilities	1,099		1,170
Other derivative liabilities	28	[5]	31	[6]
Total financial liabilities at fair value	1,127		1,201
Designated as Hedging Instrument [Member] | Fair Value, Measurements, Recurring [Member]
Fixed maturities:
Other derivative assets	6		5
Non designated [Member] | Fair Value, Measurements, Recurring [Member]
Fixed maturities:
Other derivative assets	1		36
Fair Value Inputs Level 1 [Member] | Fair Value, Measurements, Recurring [Member]
Fixed maturities:
Federal government and agency	132		156
State and local government	0		0
Foreign government	0		0
Corporate	0		0
Federal agency mortgage-backed	0		0
Other mortgage-backed	0		0
Other asset-backed	0		0
Total fixed maturities	132	[1]	156	[2]
Equity securities	6		4
Subtotal	138		160
Short-term investments	0		0
GMIB assets	0	[3]	0	[4]
Other derivative assets	0	[5]	0	[6]
Total financial assets at fair value, excluding separate accounts	138		160
Financial liabilities at fair value:
GMIB liabilities	0		0
Other derivative liabilities	0	[5]	0	[6]
Total financial liabilities at fair value	0		0
Fair Value Inputs Level 2 [Member] | Fair Value, Measurements, Recurring [Member]
Fixed maturities:
Federal government and agency	715		746
State and local government	2,401		2,437
Foreign government	1,218		1,298
Corporate	10,422		11,201
Federal agency mortgage-backed	107		122
Other mortgage-backed	82		88
Other asset-backed	269		340
Total fixed maturities	15,214	[1]	16,232	[2]
Equity securities	91		73
Subtotal	15,305		16,305
Short-term investments	122		154
GMIB assets	0	[3]	0	[4]
Other derivative assets	7	[5]	41	[6]
Total financial assets at fair value, excluding separate accounts	15,434		16,500
Financial liabilities at fair value:
GMIB liabilities	0		0
Other derivative liabilities	28	[5]	31	[6]
Total financial liabilities at fair value	28		31
Fair Value Inputs Level 3 [Member]
Financial liabilities at fair value:
Unrealized Appreciation Settlement Annuity	103		108
Fair Value Inputs Level 3 [Member] | Fair Value, Measurements, Recurring [Member]
Fixed maturities:
Federal government and agency	0		0
State and local government	0		0
Foreign government	24		24
Corporate	584		695
Federal agency mortgage-backed	0		0
Other mortgage-backed	1		1
Other asset-backed	645		597
Total fixed maturities	1,254	[1]	1,317	[2]
Equity securities	34		34
Subtotal	1,288		1,351
Short-term investments	0		0
GMIB assets	1,117	[3]	622	[4]
Other derivative assets	0	[5]	0	[6]
Total financial assets at fair value, excluding separate accounts	2,405		1,973
Financial liabilities at fair value:
GMIB liabilities	1,099		1,170
Other derivative liabilities	0	[5]	0	[6]
Total financial liabilities at fair value	$ 1,099		$ 1,170

[1] Fixed maturities included $810 million of net appreciation required to adjust future policy benefits for the run-off settlement annuity business including $103 million of appreciation for securities classified in Level 3.

[2] Fixed maturities included $875 million of net appreciation required to adjust future policy benefits for the run-off settlement annuity business including $108 million of appreciation for securities classified in Level 3.

[3] The GMIB assets represent retrocessional contracts in place from three external reinsurers that cover the exposures on these contracts.

[4] The GMIB assets represent retrocessional contracts in place from two external reinsurers that covered 55% of the exposures on these contracts.

[5] Other derivative assets included $6 million of interest rate and foreign currency swaps qualifying as cash flow hedges and $1 million of interest rate swaps not designated as accounting hedges. Other derivative liabilities reflected foreign currency and interest rate swaps qualifying as cash flow hedges. See Note 10 for additional information.

[6] Other derivative assets included $5 million of interest rate and foreign currency swaps qualifying as cash flow hedges and $36 million of interest rate swaps not designated as accounting hedges. Other derivative liabilities reflected foreign currency and interest rate swaps qualifying as cash flow hedges. See Note 10 for additional information.