Investments (Fixed Maturity and Equity Securities Available-For-Sale by Sector) (Details) (USD $) In Millions, unless otherwise specified	Sep. 30, 2013	Dec. 31, 2012	Dec. 31, 2011
Available-for-sale Securities [Abstract]
Amortized Cost	$ 43,660	$ 46,005
Cost or Amortized Cost	388	311
Gross Unrealized OTTI Loss	44	64	125
Fixed maturity securities available-for-sale, at estimated fair value (amortized cost: $43,660 and $46,005, respectively)	45,930	50,968
Equity securities	397	317
Fixed maturity securities [Member]
Available-for-sale Securities [Abstract]
Amortized Cost	43,660	46,005
Available For Sale Securities Gross Unrealized Gain Accumulated Investments	2,885	5,238
Available For Sale Securities, Gross Unrealized Loss Accumulated Investments	571	211
Gross Unrealized OTTI Loss	44	64
Fixed maturity securities available-for-sale, at estimated fair value (amortized cost: $43,660 and $46,005, respectively)	45,930	50,968
U.S. corporate securities [Member]
Available-for-sale Securities [Abstract]
Amortized Cost	16,405	16,914
Available For Sale Securities Gross Unrealized Gain Accumulated Investments	1,258	2,063
Available For Sale Securities, Gross Unrealized Loss Accumulated Investments	215	82
Gross Unrealized OTTI Loss	0	0
Fixed maturity securities available-for-sale, at estimated fair value (amortized cost: $43,660 and $46,005, respectively)	17,448	18,895
U.S. Treasury and agency securities [Member]
Available-for-sale Securities [Abstract]
Amortized Cost	7,425	7,678
Available For Sale Securities Gross Unrealized Gain Accumulated Investments	484	1,186
Available For Sale Securities, Gross Unrealized Loss Accumulated Investments	153	0
Gross Unrealized OTTI Loss	0	0
Fixed maturity securities available-for-sale, at estimated fair value (amortized cost: $43,660 and $46,005, respectively)	7,756	8,864
Foreign corporate securities [Member]
Available-for-sale Securities [Abstract]
Amortized Cost	8,332	8,618
Available For Sale Securities Gross Unrealized Gain Accumulated Investments	531	853
Available For Sale Securities, Gross Unrealized Loss Accumulated Investments	68	26
Gross Unrealized OTTI Loss	0	0
Fixed maturity securities available-for-sale, at estimated fair value (amortized cost: $43,660 and $46,005, respectively)	8,795	9,445
RMBS [Member]
Available-for-sale Securities [Abstract]
Amortized Cost	4,971	5,492
Available For Sale Securities Gross Unrealized Gain Accumulated Investments	237	360
Available For Sale Securities, Gross Unrealized Loss Accumulated Investments	60	50
Gross Unrealized OTTI Loss	44	64
Fixed maturity securities available-for-sale, at estimated fair value (amortized cost: $43,660 and $46,005, respectively)	5,104	5,738
ABS [Member]
Available-for-sale Securities [Abstract]
Amortized Cost	1,924	2,204
Available For Sale Securities Gross Unrealized Gain Accumulated Investments	35	67
Available For Sale Securities, Gross Unrealized Loss Accumulated Investments	11	18
Gross Unrealized OTTI Loss	0	0
Fixed maturity securities available-for-sale, at estimated fair value (amortized cost: $43,660 and $46,005, respectively)	1,948	2,253
State and political subdivision securities [Member]
Available-for-sale Securities [Abstract]
Amortized Cost	2,014	2,002
Available For Sale Securities Gross Unrealized Gain Accumulated Investments	153	354
Available For Sale Securities, Gross Unrealized Loss Accumulated Investments	45	27
Gross Unrealized OTTI Loss	0	0
Fixed maturity securities available-for-sale, at estimated fair value (amortized cost: $43,660 and $46,005, respectively)	2,122	2,329
CMBS [Member]
Available-for-sale Securities [Abstract]
Amortized Cost	1,597	2,221
Available For Sale Securities Gross Unrealized Gain Accumulated Investments	70	141
Available For Sale Securities, Gross Unrealized Loss Accumulated Investments	4	6
Gross Unrealized OTTI Loss	0	0
Fixed maturity securities available-for-sale, at estimated fair value (amortized cost: $43,660 and $46,005, respectively)	1,663	2,356
Foreign government debt securities [Member]
Available-for-sale Securities [Abstract]
Amortized Cost	992	876
Available For Sale Securities Gross Unrealized Gain Accumulated Investments	117	214
Available For Sale Securities, Gross Unrealized Loss Accumulated Investments	15	2
Gross Unrealized OTTI Loss	0	0
Fixed maturity securities available-for-sale, at estimated fair value (amortized cost: $43,660 and $46,005, respectively)	1,094	1,088
Equity Securities [Member]
Available-for-sale Securities [Abstract]
Cost or Amortized Cost	388	311
Available For Sale Securities Gross Unrealized Gain Accumulated Investments	39	29
Available For Sale Securities, Gross Unrealized Loss Accumulated Investments	30	23
Gross Unrealized OTTI Loss	0	0
Equity securities	397	317
Non-redeemable preferred stock [Member]
Available-for-sale Securities [Abstract]
Cost or Amortized Cost	229	151
Available For Sale Securities Gross Unrealized Gain Accumulated Investments	6	11
Available For Sale Securities, Gross Unrealized Loss Accumulated Investments	27	22
Gross Unrealized OTTI Loss	0	0
Equity securities	208	140
Common Stock [Member]
Available-for-sale Securities [Abstract]
Cost or Amortized Cost	159	160
Available For Sale Securities Gross Unrealized Gain Accumulated Investments	33	18
Available For Sale Securities, Gross Unrealized Loss Accumulated Investments	3	1
Gross Unrealized OTTI Loss	0	0
Equity securities	$ 189	$ 177