Related Party (Affiliated Asset Transfers) (Details) (USD $) In Millions, unless otherwise specified	3 Months Ended		6 Months Ended	12 Months Ended
	Mar. 31, 2013	Mar. 31, 2012	Jun. 30, 2013	Dec. 31, 2012
Related Party Transactions [Line Items]
Fixed maturity asset transfer amortized cost				$ 27
Fixed maturity asset transfer fair value				28
Realized gain on fixed maturity asset transfer				1
Commercial mortgage loans asset transfer amortized cost	90	123	27
Commercial mortgage loans asset transfer fair value	103	141	28
Realized gain on commerical mortgage loan asset transfer	$ 8	$ 11	$ 1