Short And Long-Term Debt Other Debt Facilities (Details) - USD ($) $ in Millions	1 Months Ended
	Aug. 31, 2015	Sep. 30, 2015	Dec. 31, 2014	Mar. 05, 2013
Line of Credit Facility [Line Items]
Letter of Credit, borrowing capacity				$ 250
Outstanding letters of credit		$ 135
Unsecured Letter of Credit Facility [Member]
Line of Credit Facility [Line Items]
Increase in borrowing capacity	$ 7
Letter of Credit, borrowing capacity		88	$ 81
Outstanding letters of credit		82
June 2017 [Member] \| Unsecured Letter of Credit Facility [Member]
Line of Credit Facility [Line Items]
Letter of Credit, borrowing capacity		27
August 2017 [Member] \| Unsecured Letter of Credit Facility [Member]
Line of Credit Facility [Line Items]
Letter of Credit, borrowing capacity		54
September 2018 [Member] \| Unsecured Letter of Credit Facility [Member]
Line of Credit Facility [Line Items]
Letter of Credit, borrowing capacity		$ 7