Investments (Mortgage Loans and Valuation Allowance by Portfolio Segment) (Details) (USD $) In Millions, unless otherwise specified	Jun. 30, 2014	Mar. 31, 2014	Dec. 31, 2013	Jun. 30, 2013	Mar. 31, 2013	Dec. 31, 2012
Mortgage Loans on Real Estate [Line Items]
Evaluated individually for credit losses	$ 499		$ 622
Evaluated collectively for credit losses	56,013		55,467
Total mortgage loans	56,512		56,089
Specific credit losses	39		66
Non-specifically identified credit losses	255		256
Valuation allowances	294	326	322	302	332	347
Mortgage loan, net of valuation allowance	56,218		55,767
Commercial mortgage loans portfolio segment [Member]
Mortgage Loans on Real Estate [Line Items]
Evaluated individually for credit losses	415		506
Evaluated collectively for credit losses	40,189		40,420
Total mortgage loans	40,604		40,926
Specific credit losses	33		58
Non-specifically identified credit losses	197		200
Valuation allowances	230	259	258	242	275	293
Mortgage loan, net of valuation allowance	40,374		40,668
Agricultural [Member]
Mortgage Loans on Real Estate [Line Items]
Evaluated individually for credit losses	75		100
Evaluated collectively for credit losses	11,886		12,291
Total mortgage loans	11,961		12,391
Specific credit losses	6		7
Non-specifically identified credit losses	36		37
Valuation allowances	42	42	44	49	54	52
Mortgage loan, net of valuation allowance	11,919		12,347
Residential [Member]
Mortgage Loans on Real Estate [Line Items]
Evaluated individually for credit losses	9		16
Evaluated collectively for credit losses	3,938		2,756
Total mortgage loans	3,947		2,772
Specific credit losses	0		1
Non-specifically identified credit losses	22		19
Valuation allowances	22	25	20	11	3	2
Mortgage loan, net of valuation allowance	$ 3,925		$ 2,752