Segment Information (Unaudited) Segment Information (Unaudited) (Details 2) (USD $) In Millions, unless otherwise specified	3 Months Ended	9 Months Ended
Sep. 30, 2014	Sep. 30, 2013	Sep. 30, 2014	Sep. 30, 2013
Change in Accounting Estimate [Line Items]
Operating income	$ 769	$ 790	$ 2,434	$ 2,355
Change in Assumptions for Pension Plans [Member]
Change in Accounting Estimate [Line Items]
Operating income	$ (132)		$ (132)

The net result for the period of deducting operating expenses from operating revenues.

No definition available.

Name:	us-gaap_OperatingIncomeLoss
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration