Financing (Commercial Paper Programs And Credit Facilities) (Narrative) (Details) - USD ($)			12 Months Ended
	Dec. 31, 2017	Jul. 10, 2015	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Line of Credit Facility [Line Items]
Debt discounts, premiums and debt issuance costs	$ 25,000,000		$ 25,000,000	$ 25,000,000
Long-term debt	10,522,100,000		10,522,100,000	12,269,000,000
Credit facility, borrowings outstanding	$ 0		$ 0
Commercial paper
Line of Credit Facility [Line Items]
Debt, weighted average annual interest rate, basis points	0.01%		0.01%
Long-term debt weighted average maturity	50 days
Long-term debt	$ 2,400,000,000		$ 2,400,000,000
1.65% senior unsecured notes due 2018 | Senior notes
Line of Credit Facility [Line Items]
Long-term debt	499,200,000		499,200,000	498,100,000
Debt instrument, face amount	$ 500,000,000		$ 500,000,000
Revolving credit facility
Line of Credit Facility [Line Items]
Consolidated leverage ratio	0.65		0.65
Revolving credit facility | Federal funds rate
Line of Credit Facility [Line Items]
Basis spread percentage to determine floating interest rate	0.50%
Revolving credit facility | LIBOR-based rate
Line of Credit Facility [Line Items]
Basis spread percentage to determine floating interest rate	1.00%
Revolving credit facility | Credit Facility | Long-term debt
Line of Credit Facility [Line Items]
Line of credit, maximum borrowing capacity					$ 4,000,000,000
Debt instrument, extension option, term		1 year
Line of credit facility, maximum amount outstanding during period			$ 0
Revolving credit facility | 364-Day Facility | Short-term debt
Line of Credit Facility [Line Items]
Line of credit, maximum borrowing capacity				$ 3,000,000,000
Line of credit facility, maximum amount outstanding during period			$ 0