General - Statement of Cash Flows (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2019	Sep. 30, 2018
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Net income	$ 931	$ 979	$ 3,074	$ 2,702
Pension and other postretirement remeasurement gains and losses	225	(39)	365	(32)
Income taxes			254	(178)
Other operating assets and liabilities			(181)	335
Net cash provided by operating activities			3,895	3,818
Previously reported
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Net income	1,071	870	3,278	2,521
Pension and other postretirement remeasurement gains and losses			0	0
Income taxes			309	(227)
Other operating assets and liabilities			(75)	533
Net cash provided by operating activities			3,895	3,818
Impact of change | Impact of change
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Net income	$ (140)	$ 109	(204)	181
Pension and other postretirement remeasurement gains and losses			365	(32)
Income taxes			(55)	49
Other operating assets and liabilities			(106)	(198)
Net cash provided by operating activities			$ 0	$ 0