Investments (Fixed Maturity and Eqiuty Securities Available-For-Sale - Narrative) (Details) (USD $) In Millions, unless otherwise specified	Mar. 31, 2013	Dec. 31, 2012	Dec. 31, 2011
Summary of Certain Fixed Maturity Securities
Available-for-sale Securities, Debt Securities	$ 374,294	$ 374,266
Gross Unrealized OTTI Loss	260	361	724
Foreign corporate securities [Member]
Summary of Certain Fixed Maturity Securities
Available-for-sale Securities, Debt Securities	66,086	67,184
Net unrealized gains (losses)	5,322	5,654
Gross Unrealized OTTI Loss	(2)	(1)
Non-income producing fixed maturity securities [Member]
Summary of Certain Fixed Maturity Securities
Available-for-sale Securities, Debt Securities	80	85
Net unrealized gains (losses)	$ 19	$ 11

Amount of debt securities categorized neither as held-to-maturity nor trading.

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