Significant Accounting Policies - Consolidated Statement of Cash Flow as Adjusted (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2021	Sep. 30, 2020
Cash Flows from Operating Activities
Net income including noncontrolling interest	$ 1,437	$ 1,434	$ 4,589	$ 4,047
Company pension and postretirement expense			137	232
Other — net			$ 212	4
Under Prior Method
Cash Flows from Operating Activities
Net income including noncontrolling interest		$ 1,417		3,998
Company pension and postretirement expense				295
Other — net				$ (10)