Investments (Contractual Maturity Dates For Fixed-Maturity And Short-Term Investments) (Details) (USD $) In Millions, unless otherwise specified	Dec. 31, 2014	Dec. 31, 2013
Amortized cost
Less than 1 year	$ 502
Years 1 - 5	3,404
Years 5 - 10	3,322
Due after ten years	1,643
Total	8,871	8,638
Fair value
Less than 1 year	509
Years 1 - 5	3,687
Years 5 - 10	3,506
Due after ten years	1,758
Total	$ 9,460	$ 9,121
% of fair value
Less than 1 year	5.40%
Years 1 - 5	39.00%
Years 5 - 10	37.00%
Due after ten years	18.60%
Total	100.00%