Investments (Fixed Maturity and Equity Securities Available-For-Sale - Narrative) (Details) (USD $) In Millions, unless otherwise specified	Sep. 30, 2013	Dec. 31, 2012	Dec. 31, 2011
Summary of Certain Fixed Maturity Securities
Gross Unrealized OTTI Loss	$ 241	$ 361	$ 724
Available-for-sale Securities, Debt Securities	348,787	374,266
Foreign corporate securities [Member]
Summary of Certain Fixed Maturity Securities
Gross Unrealized OTTI Loss	0	(1)
Available-for-sale Securities, Debt Securities	63,648	67,184
Gross Unrealized Gain	3,871	5,654
Non-income producing fixed maturity securities [Member]
Summary of Certain Fixed Maturity Securities
Available-for-sale Securities, Debt Securities	60	85
Gross Unrealized Gain	$ 25	$ 11