Investments (Mortgage Loans by Portfolio Segment) (Details) (USD $) In Millions, unless otherwise specified	Sep. 30, 2013	Jun. 30, 2013	Dec. 31, 2012	Sep. 30, 2012	Jun. 30, 2012	Dec. 31, 2011
Notes, Loans and Financing Receivable, Net, Current [Abstract]
Commercial mortgage loans	$ 5,114		$ 5,266
Percentage of loans receivable on commercial mortgage loans	59.90%		57.50%
Agricultural mortgage loans	1,310		1,260
Percentage of loans receivable on agricultural mortgage loans	15.30%		13.80%
Subtotal	6,424		6,526
Percentage of loans receivable on subtotal	75.20%		71.30%
Valuation allowances	(34)	(34)	(35)	(41)	(42)	(61)
Percentage of loans receivable on valuation allowances	(0.40%)		(0.40%)
Subtotal mortgage loans, net	6,390		6,491
Percentage of loans receivable on subtotal mortgage loans held-for-investment, net	74.80%		70.90%
Commercial mortgage loans held by consolidated securitization entities - fair value option	2,096		2,666
Percentage of loans receivable on commercial mortgage loans held by consolidated securitization entities - fair value option	24.50%		29.10%
Mortgage loans, at estimated fair value, relating to variable interest entities	8,486		9,157
Percentage Of Mortgage Loans On Real Estate Commercial And Consumer Net To Mortgage Loans On Real Estate Commercial And Consumer Net	99.30%		100.00%
Mortgage loans held-for-sale	63		0
Percentage Of mortgage loans held-for-sale	0.70%		0.00%
Mortgage loans (net of valuation allowances of $34 and $35, respectively; includes $2,096 and $2,666, respectively, at estimated fair value, relating to variable interest entities)	$ 8,549		$ 9,157
Percentage of total mortgage loans, net	100.00%		100.00%