Fair Value (Carrying And Estimated Fair Values by Level Of Financial Instruments Not Recorded At Fair Value On Consolidated Balance Sheet) (Details) - USD ($) $ in Millions	Sep. 30, 2019	Dec. 31, 2018
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Other invested assets, long-term	$ 3,914	$ 3,726
Short-term borrowings	710	1,145
Commercial paper	500	697
Notes	20,198	17,145
Convertible debentures	893	1,030
Fair Value, Recurring [Member] | Level III [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Other invested assets, long-term	3,914	3,726
Short-term borrowings	0	0
Commercial paper	0	0
Notes	0	0
Convertible debentures	0	0
Fair Value, Recurring [Member] | Level II [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Other invested assets, long-term	0	0
Short-term borrowings	710	1,145
Commercial paper	500	697
Notes	20,198	17,145
Convertible debentures	893	1,030
Fair Value, Recurring [Member] | Level I [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Other invested assets, long-term	0	0
Short-term borrowings	0	0
Commercial paper	0	0
Notes	0	0
Convertible debentures	0	0
Fair Value, Nonrecurring [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Other invested assets, long-term	3,914	3,726
Short-term borrowings	710	1,145
Commercial paper	500	697
Notes	18,841	17,178
Convertible debentures	$ 179	$ 191