Investments (Fixed Maturity and Eqiuty Securities Available-For-Sale by Sector) (Details) (USD $) In Millions, unless otherwise specified	Mar. 31, 2013	Dec. 31, 2012	Dec. 31, 2011
Available-for-sale Securities [Abstract]
Amortized Cost	$ 342,533	$ 340,870
Cost or Amortized Cost	2,898	2,838
Gross Unrealized OTTI Loss	260	361	724
Fixed maturity securities available-for-sale, at estimated fair value (amortized cost: $342,533 and $340,870, respectively; includes $3,873 and $3,378, respectively, relating to variable interest entities)	374,294	374,266
Equity securities	3,188	2,891
Fixed maturity securities [Member]
Available-for-sale Securities [Abstract]
Amortized Cost	342,533	340,870
Gross Unrealized Gain	33,326	35,144
Gross Unrealized Temporary Loss	1,305	1,387
Gross Unrealized OTTI Loss	260	361
Fixed maturity securities available-for-sale, at estimated fair value (amortized cost: $342,533 and $340,870, respectively; includes $3,873 and $3,378, respectively, relating to variable interest entities)	374,294	374,266
U.S. corporate securities [Member]
Available-for-sale Securities [Abstract]
Amortized Cost	102,086	102,669
Gross Unrealized Gain	11,364	11,887
Gross Unrealized Temporary Loss	444	430
Gross Unrealized OTTI Loss	0	0
Fixed maturity securities available-for-sale, at estimated fair value (amortized cost: $342,533 and $340,870, respectively; includes $3,873 and $3,378, respectively, relating to variable interest entities)	113,006	114,126
Foreign corporate securities [Member]
Available-for-sale Securities [Abstract]
Amortized Cost	61,067	61,806
Gross Unrealized Gain	5,322	5,654
Gross Unrealized Temporary Loss	305	277
Gross Unrealized OTTI Loss	(2)	(1)
Fixed maturity securities available-for-sale, at estimated fair value (amortized cost: $342,533 and $340,870, respectively; includes $3,873 and $3,378, respectively, relating to variable interest entities)	66,086	67,184
Foreign government debt securities [Member]
Available-for-sale Securities [Abstract]
Amortized Cost	49,951	51,967
Gross Unrealized Gain	5,552	5,440
Gross Unrealized Temporary Loss	68	71
Gross Unrealized OTTI Loss	0	0
Fixed maturity securities available-for-sale, at estimated fair value (amortized cost: $342,533 and $340,870, respectively; includes $3,873 and $3,378, respectively, relating to variable interest entities)	55,435	57,336
RMBS [Member]
Available-for-sale Securities [Abstract]
Amortized Cost	34,403	35,666
Gross Unrealized Gain	2,391	2,477
Gross Unrealized Temporary Loss	198	315
Gross Unrealized OTTI Loss	249	349
Fixed maturity securities available-for-sale, at estimated fair value (amortized cost: $342,533 and $340,870, respectively; includes $3,873 and $3,378, respectively, relating to variable interest entities)	36,347	37,479
U.S. Treasury and agency securities [Member]
Available-for-sale Securities [Abstract]
Amortized Cost	49,258	41,874
Gross Unrealized Gain	5,229	6,104
Gross Unrealized Temporary Loss	30	11
Gross Unrealized OTTI Loss	0	0
Fixed maturity securities available-for-sale, at estimated fair value (amortized cost: $342,533 and $340,870, respectively; includes $3,873 and $3,378, respectively, relating to variable interest entities)	54,457	47,967
CMBS [Member]
Available-for-sale Securities [Abstract]
Amortized Cost	17,015	18,177
Gross Unrealized Gain	935	1,009
Gross Unrealized Temporary Loss	53	57
Gross Unrealized OTTI Loss	0	0
Fixed maturity securities available-for-sale, at estimated fair value (amortized cost: $342,533 and $340,870, respectively; includes $3,873 and $3,378, respectively, relating to variable interest entities)	17,897	19,129
ABS [Member]
Available-for-sale Securities [Abstract]
Amortized Cost	15,841	15,762
Gross Unrealized Gain	423	404
Gross Unrealized Temporary Loss	137	156
Gross Unrealized OTTI Loss	13	13
Fixed maturity securities available-for-sale, at estimated fair value (amortized cost: $342,533 and $340,870, respectively; includes $3,873 and $3,378, respectively, relating to variable interest entities)	16,114	15,997
State and political subdivision securities [Member]
Available-for-sale Securities [Abstract]
Amortized Cost	12,912	12,949
Gross Unrealized Gain	2,110	2,169
Gross Unrealized Temporary Loss	70	70
Gross Unrealized OTTI Loss	0	0
Fixed maturity securities available-for-sale, at estimated fair value (amortized cost: $342,533 and $340,870, respectively; includes $3,873 and $3,378, respectively, relating to variable interest entities)	14,952	15,048
Equity Securities [Member]
Available-for-sale Securities [Abstract]
Cost or Amortized Cost	2,898	2,838
Gross Unrealized Gain	376	212
Gross Unrealized Temporary Loss	86	159
Gross Unrealized OTTI Loss	0	0
Equity securities	3,188	2,891
Common Stock [Member]
Available-for-sale Securities [Abstract]
Cost or Amortized Cost	1,985	2,034
Gross Unrealized Gain	305	147
Gross Unrealized Temporary Loss	8	19
Gross Unrealized OTTI Loss	0	0
Equity securities	2,282	2,162
Non-redeemable preferred stock [Member]
Available-for-sale Securities [Abstract]
Cost or Amortized Cost	913	804
Gross Unrealized Gain	71	65
Gross Unrealized Temporary Loss	78	140
Gross Unrealized OTTI Loss	0	0
Equity securities	$ 906	$ 729