Investments (Credit loss of OTTI recognized in OCI on fixed maturity AFS securities) (Details) (USD $) In Millions, unless otherwise specified	12 Months Ended
	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
Other Than Temporary Credit Loss Recognized In Earnings Roll Forward [Abstract]
Balance as of beginning of year	$ 390	$ 319	$ 268
Increases attributable to:
Credit losses on securities for which an OTTI was not previously recognized	108	55	14
Credit losses on securities for which an OTTI was previously recognized	62	71	65
Decreases attributable to:
Securities sold	(136)	(55)	(28)
Balance as of end of year	$ 424	$ 390	$ 319