Basis of Presentation (Details) (USD $) In Millions, unless otherwise specified	9 Months Ended
	Sep. 30, 2013 state	Sep. 30, 2012
Number of states in which service is provided (states)	14
Net cash provided by operating activities	$ 2,032	$ 2,079
Net cash used in investing activities	(1,075)	(1,296)
Net cash used in financing activities	(952)	(777)
Correction of presentation of certain transactions with affiliates in consolidated statements of cash flows | As Reported
Net cash provided by operating activities		2,713
Net cash used in investing activities		(1,784)
Net cash used in financing activities		(923)
Correction of presentation of certain transactions with affiliates in consolidated statements of cash flows | Error Correction
Net cash provided by operating activities		(634)
Net cash used in investing activities		488
Net cash used in financing activities		$ 146