Commercial Paper and Long-Term Debt (Narrative) (Details) - USD ($) $ in Millions	6 Months Ended
	Jun. 30, 2019	Dec. 31, 2018
Minimum [Member] | Revolving Credit Facility [Member]
Debt Instrument [Line Items]
Line of Credit Facility, Interest Rate at Period End	2.90%
Maximum [Member] | Revolving Credit Facility [Member]
Debt Instrument [Line Items]
Line of Credit Facility, Interest Rate at Period End	3.10%
Five Year $3.5 Billion Credit Facility [Member] | Revolving Credit Facility [Member]
Debt Instrument [Line Items]
Long-term Line of Credit	$ 0
Line of Credit, Credit Facility, Maximum Borrowing Capacity	$ 3,500
Line of Credit Facility, Expiration Period	5 years
Three Year $3.5 Billion Credit Facility [Member] | Revolving Credit Facility [Member]
Debt Instrument [Line Items]
Long-term Line of Credit	$ 0
Line of Credit, Credit Facility, Maximum Borrowing Capacity	$ 3,500
Line of Credit Facility, Expiration Period	3 years
364 Day $3.0 Billion Credit Facility [Member] | Revolving Credit Facility [Member]
Debt Instrument [Line Items]
Line of Credit, Current	$ 0
Line of Credit, Credit Facility, Maximum Borrowing Capacity	$ 3,000
Line of Credit Facility, Expiration Period	364 days
364 Day $2.5 Billion Credit Facility [Member] | Revolving Credit Facility [Member]
Debt Instrument [Line Items]
Line of Credit, Current	$ 0
Line of Credit, Credit Facility, Maximum Borrowing Capacity	$ 2,500
Line of Credit Facility, Expiration Period	364 days
Subsidiaries [Member]
Debt Instrument [Line Items]
Other Long-term Debt	$ 1,200	$ 1,300
Other Long-term Debt, Current	$ 329	$ 229
Commercial Paper [Member]
Debt Instrument [Line Items]
Short-term Debt, Weighted Average Interest Rate, at Point in Time	2.60%