Investments (Fixed Maturity and Equity Securities Available-For-Sale by Sector) (Details) (USD $) In Millions, unless otherwise specified	Jun. 30, 2013	Dec. 31, 2012	Dec. 31, 2011
Available-for-sale Securities [Abstract]
Amortized Cost	$ 46,427	$ 46,005
Cost or Amortized Cost	399	311
Gross Unrealized OTTI Loss	52	64	125
Fixed maturity securities available-for-sale, at estimated fair value (amortized cost: $46,427 and $46,005, respectively)	48,963	50,968
Equity securities	420	317
Fixed maturity securities [Member]
Available-for-sale Securities [Abstract]
Amortized Cost	46,427	46,005
Gross Unrealized Gain	3,130	5,238
Gross Unrealized Temporary Loss	542	211
Gross Unrealized OTTI Loss	52	64
Fixed maturity securities available-for-sale, at estimated fair value (amortized cost: $46,427 and $46,005, respectively)	48,963	50,968
U.S. corporate securities [Member]
Available-for-sale Securities [Abstract]
Amortized Cost	16,910	16,914
Gross Unrealized Gain	1,317	2,063
Gross Unrealized Temporary Loss	195	82
Gross Unrealized OTTI Loss	0	0
Fixed maturity securities available-for-sale, at estimated fair value (amortized cost: $46,427 and $46,005, respectively)	18,032	18,895
U.S. Treasury and agency securities [Member]
Available-for-sale Securities [Abstract]
Amortized Cost	8,820	7,678
Gross Unrealized Gain	641	1,186
Gross Unrealized Temporary Loss	125	0
Gross Unrealized OTTI Loss	0	0
Fixed maturity securities available-for-sale, at estimated fair value (amortized cost: $46,427 and $46,005, respectively)	9,336	8,864
Foreign corporate securities [Member]
Available-for-sale Securities [Abstract]
Amortized Cost	8,506	8,618
Gross Unrealized Gain	494	853
Gross Unrealized Temporary Loss	89	26
Gross Unrealized OTTI Loss	0	0
Fixed maturity securities available-for-sale, at estimated fair value (amortized cost: $46,427 and $46,005, respectively)	8,911	9,445
RMBS [Member]
Available-for-sale Securities [Abstract]
Amortized Cost	5,163	5,492
Gross Unrealized Gain	244	360
Gross Unrealized Temporary Loss	68	50
Gross Unrealized OTTI Loss	52	64
Fixed maturity securities available-for-sale, at estimated fair value (amortized cost: $46,427 and $46,005, respectively)	5,287	5,738
ABS [Member]
Available-for-sale Securities [Abstract]
Amortized Cost	2,385	2,204
Gross Unrealized Gain	40	67
Gross Unrealized Temporary Loss	13	18
Gross Unrealized OTTI Loss	0	0
Fixed maturity securities available-for-sale, at estimated fair value (amortized cost: $46,427 and $46,005, respectively)	2,412	2,253
State and political subdivision securities [Member]
Available-for-sale Securities [Abstract]
Amortized Cost	1,986	2,002
Gross Unrealized Gain	192	354
Gross Unrealized Temporary Loss	31	27
Gross Unrealized OTTI Loss	0	0
Fixed maturity securities available-for-sale, at estimated fair value (amortized cost: $46,427 and $46,005, respectively)	2,147	2,329
CMBS [Member]
Available-for-sale Securities [Abstract]
Amortized Cost	1,734	2,221
Gross Unrealized Gain	79	141
Gross Unrealized Temporary Loss	6	6
Gross Unrealized OTTI Loss	0	0
Fixed maturity securities available-for-sale, at estimated fair value (amortized cost: $46,427 and $46,005, respectively)	1,807	2,356
Foreign government debt securities [Member]
Available-for-sale Securities [Abstract]
Amortized Cost	923	876
Gross Unrealized Gain	123	214
Gross Unrealized Temporary Loss	15	2
Gross Unrealized OTTI Loss	0	0
Fixed maturity securities available-for-sale, at estimated fair value (amortized cost: $46,427 and $46,005, respectively)	1,031	1,088
Equity Securities [Member]
Available-for-sale Securities [Abstract]
Cost or Amortized Cost	399	311
Gross Unrealized Gain	40	29
Gross Unrealized Temporary Loss	19	23
Gross Unrealized OTTI Loss	0	0
Equity securities	420	317
Non-redeemable preferred stock [Member]
Available-for-sale Securities [Abstract]
Cost or Amortized Cost	234	151
Gross Unrealized Gain	6	11
Gross Unrealized Temporary Loss	16	22
Gross Unrealized OTTI Loss	0	0
Equity securities	224	140
Common Stock [Member]
Available-for-sale Securities [Abstract]
Cost or Amortized Cost	165	160
Gross Unrealized Gain	34	18
Gross Unrealized Temporary Loss	3	1
Gross Unrealized OTTI Loss	0	0
Equity securities	$ 196	$ 177