Derivatives (Changes in Estimated Fair Value Related to Embedded Derivatives) (Details) (USD $) In Millions, unless otherwise specified	3 Months Ended		9 Months Ended
	Sep. 30, 2013	Sep. 30, 2012	Sep. 30, 2013	Sep. 30, 2012
Derivative Instruments, Gain (Loss) [Line Items]
Net derivatives gains (losses)	$ (16)	$ 91	$ 165	$ 270
Net derivatives gains (losses) [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Net derivatives gains (losses)	$ (16)	$ 91	$ 165	$ 270