Fair Value Measurement (Details) (USD $) In Millions, unless otherwise specified	3 Months Ended		6 Months Ended	12 Months Ended	6 Months Ended	12 Months Ended	3 Months Ended																3 Months Ended	12 Months Ended	3 Months Ended	12 Months Ended
	Jun. 30, 2013 Security	Dec. 31, 2012	Jun. 30, 2013 Minimum	Dec. 31, 2012 Minimum	Jun. 30, 2013 Maximum	Dec. 31, 2012 Maximum	Jun. 30, 2013 CDS contracts		Dec. 31, 2012 CDS contracts		Jun. 30, 2013 CDS contracts Based on actual collateral specific spreads		Dec. 31, 2012 CDS contracts Based on actual collateral specific spreads		Jun. 30, 2013 CDS contracts Based on market indices		Dec. 31, 2012 CDS contracts Based on market indices		Jun. 30, 2013 CDS contracts Provided by the CDS counterparty		Dec. 31, 2012 CDS contracts Provided by the CDS counterparty		Jun. 30, 2013 CDS contracts Minimum	Dec. 31, 2012 CDS contracts Minimum	Jun. 30, 2013 CDS contracts Maximum	Dec. 31, 2012 CDS contracts Maximum	Jun. 30, 2013 Scenario 1 CDS contracts	Jun. 30, 2013 Scenario 1 CDS contracts AGC	Jun. 30, 2013 Scenario 2 CDS contracts	Jun. 30, 2013 Scenario 2 CDS contracts AGC	Jun. 30, 2013 Level 3 Fair value measurement on recurring basis	Dec. 31, 2012 Level 3 Fair value measurement on recurring basis	Jun. 30, 2013 Level 3 Fair value measurement on non-recurring basis	Dec. 31, 2012 Level 3 Fair value measurement on non-recurring basis	Jun. 30, 2013 Level 2 Fair value measurement on recurring basis	Dec. 31, 2012 Level 2 Fair value measurement on recurring basis
Credit Derivatives
Number of fixed maturity securities valued using model processes	37
Percentage of fixed maturity securities valued using model processes to the Company's fixed-income securities and short-term investments at fair value	5.80%
Fixed maturity securities																															$ 612	$ 560			$ 8,952	$ 9,496
Other investments																															2				61
Mortgage loans recorded at fair value																																	$ 6	$ 7
Discount factor (as a percent)			0.00%	0.00%	4.03%	3.28%																	0.20%	0.21%	3.45%	2.81%
Gross spread percentage							100.00%	[1]	100.00%	[1]	6.00%	[1]	6.00%	[1]	87.00%	[1]	88.00%	[1]	7.00%	[1]	6.00%	[1]
Number of sources of credit spread							3
Percentage of CDS contracts which are fair valued using minimum premium	25.00%	71.00%
Original gross spread/cash bond price (as a percent)																											1.85%	3.00%	5.00%	17.60%
Bank profit (as a percent)																											1.15%		0.50%
Hedge cost (as a percent)																											0.30%		4.40%
The Company premium received per annum (as a percent)																											0.40%		0.10%
Bank profit as % of total																											62.00%		10.00%
Hedge cost as % of total																											16.00%		88.00%
Premium received per annum as % of total																											22.00%		2.00%
Percentage of exposure hedged																												10.00%		25.00%

[1] Based on par.