Investments (Maturities of Fixed Maturity Securities) (Details) (USD $) In Millions, unless otherwise specified	Mar. 31, 2015	Dec. 31, 2014
Available-for-sale Securities, Debt Maturities [Abstract]
Due in One Year or Less	$ 3,081
Due After One Year Through Five Years	10,178
Due After Five Years Through Ten Years	7,520
Due After Ten Years	15,290
Structured Securities	12,164
Amortized cost	48,233	46,423
Due in One Year or Less	3,108
Due After One Year Through Five Years	10,611
Due After Five Years Through Ten Years	7,973
Due After Ten Years	18,870
Structured Securities	12,503
Fixed maturity securities available-for-sale, at estimated fair value (amortized cost: $48,233 and $46,423, respectively)	$ 53,065	$ 50,697