Retirement Benefits - Benefit Obligations and Plan Assets in Balance Sheet (Details) - USD ($) $ in Millions	Dec. 31, 2021	Dec. 31, 2020
Pension Plan, Defined Benefit [Member]
Defined Benefit Plan Disclosure [Line Items]
Other current liabilities	$ 29	$ 47
Pension obligations	2,990	4,503
Non-pension postretirement benefit obligations	0	0
Unfunded status (net benefit obligation less plan assets)	3,019	4,550
Other Postretirement Benefit Plan, Defined Benefit [Member]
Defined Benefit Plan Disclosure [Line Items]
Other current liabilities	42	42
Pension obligations	0	0
Non-pension postretirement benefit obligations	1,685	2,008
Unfunded status (net benefit obligation less plan assets)	$ 1,727	$ 2,050