Consolidating Financial Information (Details 2) (USD $) In Millions, unless otherwise specified	3 Months Ended		9 Months Ended
	Sep. 30, 2012	Sep. 30, 2011	Sep. 30, 2012	Sep. 30, 2011
Condensed Consolidated Statements of Comprehensive Income
Net income	$ 283	$ 267	$ 790	$ 806
Other comprehensive income, net of tax:
Defined benefit retirement plan gain (loss), net of tax expense (benefit) of $2, $1, $7 and $(1)	4	1	13	(2)
Other comprehensive loss	4	1	13	(2)
Comprehensive income	287	268	803	804
Parent [Member]
Condensed Consolidated Statements of Comprehensive Income
Net income	283	267	790	806
Other comprehensive income, net of tax:
Comprehensive income	283	267	790	806
Issuer [Member]
Condensed Consolidated Statements of Comprehensive Income
Net income	287	267	796	806
Other comprehensive income, net of tax:
Defined benefit retirement plan gain (loss), net of tax expense (benefit) of $2, $1, $7 and $(1)	4	1	13	(2)
Other comprehensive loss	4	1	13	(2)
Comprehensive income	291	268	809	804
All Other Subsidiaries [Member]
Condensed Consolidated Statements of Comprehensive Income
Net income	167	168	500	497
Other comprehensive income, net of tax:
Comprehensive income	167	168	500	497
Total Consolidating Adjustments [Member]
Condensed Consolidated Statements of Comprehensive Income
Net income	(454)	(435)	(1,296)	(1,303)
Other comprehensive income, net of tax:
Comprehensive income	$ (454)	$ (435)	$ (1,296)	$ (1,303)