Investments (Impaired Mortgage Loans) (Details) (USD $) In Millions, unless otherwise specified	3 Months Ended		9 Months Ended
	Sep. 30, 2013	Sep. 30, 2012	Sep. 30, 2013	Sep. 30, 2012	Jun. 30, 2013	Dec. 31, 2012	Jun. 30, 2012	Dec. 31, 2011
Impaired Mortgage Loans
Unpaid Principal Balance	$ 725		$ 725			$ 750
Valuation allowances	326	354	326	354	302	347	361	481
Recorded Investment	628		628			616
Average Investment	704	598	711	557
Interest Income	9	3	19	9
Loans with a Valuation Allowance [Member]
Impaired Mortgage Loans
Unpaid Principal Balance	327		327			568
Recorded Investment	318		318			556
Valuation allowances	76		76			117
Recorded Investment	242		242			439
Loans Without Valuation Allowances [Member]
Impaired Mortgage Loans
Unpaid Principal Balance	398		398			182
Recorded Investment	386		386			177
Commercial mortgage loans portfolio segment [Member]
Impaired Mortgage Loans
Unpaid Principal Balance	533		533			548
Valuation allowances	259	300	259	300	242	293	300	398
Recorded Investment	458		458			445
Average Investment	525	395	530	334
Interest Income	4	1	11	4
Commercial mortgage loans portfolio segment [Member] | Loans with a Valuation Allowance [Member]
Impaired Mortgage Loans
Unpaid Principal Balance	230		230			445
Recorded Investment	224		224			436
Valuation allowances	62		62			94
Recorded Investment	162		162			342
Commercial mortgage loans portfolio segment [Member] | Loans Without Valuation Allowances [Member]
Impaired Mortgage Loans
Unpaid Principal Balance	303		303			103
Recorded Investment	296		296			103
Agricultural [Member]
Impaired Mortgage Loans
Unpaid Principal Balance	178		178			189
Valuation allowances	50	52	50	52	49	52	59	81
Recorded Investment	158		158			160
Average Investment	165	191	167	210
Interest Income	5	2	8	5
Agricultural [Member] | Loans with a Valuation Allowance [Member]
Impaired Mortgage Loans
Unpaid Principal Balance	85		85			110
Recorded Investment	82		82			107
Valuation allowances	12		12			21
Recorded Investment	70		70			86
Agricultural [Member] | Loans Without Valuation Allowances [Member]
Impaired Mortgage Loans
Unpaid Principal Balance	93		93			79
Recorded Investment	88		88			74
Residential [Member]
Impaired Mortgage Loans
Unpaid Principal Balance	14		14			13
Valuation allowances	17	2	17	2	11	2	2	2
Recorded Investment	12		12			11
Average Investment	14	12	14	13
Interest Income	0	0	0	0
Residential [Member] | Loans with a Valuation Allowance [Member]
Impaired Mortgage Loans
Unpaid Principal Balance	12		12			13
Recorded Investment	12		12			13
Valuation allowances	2		2			2
Recorded Investment	10		10			11
Residential [Member] | Loans Without Valuation Allowances [Member]
Impaired Mortgage Loans
Unpaid Principal Balance	2		2			0
Recorded Investment	$ 2		$ 2			$ 0