Investments (Details of the amount of credit loss of OTTI recognized in OCI) (Details) (USD $) In Millions, unless otherwise specified	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010	Dec. 31, 2009
Other Than Temporary Impairments Credit Losses [Line Items]
Amortized Cost	$ 976	$ 876
Gross Unrealized Gains	27	2
Gross Unrealized Losses and OTTI	(154)	(205)
Fair Value	849	673
Balance as of end of year	424	390	319	268
Corporate bonds [Member]
Other Than Temporary Impairments Credit Losses [Line Items]
Amortized Cost	299	169
Gross Unrealized Gains	4	1
Gross Unrealized Losses and OTTI	(98)	(67)
Fair Value	205	103
Balance as of end of year	104	51
RMBS [Member]
Other Than Temporary Impairments Credit Losses [Line Items]
Amortized Cost	636	690
Gross Unrealized Gains	22	1
Gross Unrealized Losses and OTTI	(40)	(128)
Fair Value	618	563
Balance as of end of year	227	301
CMBS [Member]
Other Than Temporary Impairments Credit Losses [Line Items]
Amortized Cost	41	17
Gross Unrealized Gains	1	0
Gross Unrealized Losses and OTTI	(16)	(10)
Fair Value	26	7
Balance as of end of year	$ 93	$ 38