General - Statement of Cash Flows (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2019	Jun. 30, 2018	Jun. 30, 2019	Jun. 30, 2018
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Net income	$ 851	$ 717	$ 2,143	$ 1,723
Pension and other postretirement remeasurement gains and losses	125	(7)	140	7
Income taxes			159	(238)
Other operating assets and liabilities			(505)	(47)
Net cash provided by operating activities			2,062	2,090
Previously reported
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Net income	920	676	2,207	1,651
Pension and other postretirement remeasurement gains and losses		0	0	0
Income taxes			177	(257)
Other operating assets and liabilities			(447)	51
Net cash provided by operating activities			2,062	2,090
Impact of change | Impact of change
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Net income	$ (69)	41	(64)	72
Pension and other postretirement remeasurement gains and losses		$ (7)	140	7
Income taxes			(18)	19
Other operating assets and liabilities			(58)	(98)
Net cash provided by operating activities			$ 0	$ 0