Postretirement Benefit Plans (Rollforward of Fair Value Measurements) (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]
Beginning Balance	$ 605
Ending Balance	691	$ 605
Level 3
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]
Beginning Balance	13
Ending Balance	384	13
Hedge funds
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]
Beginning Balance	12
Ending Balance	1	12
Other | Level 3
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]
Beginning Balance	13	12
Purchases, sales, settlements	314	1
Actual return on plan assets	44
Impact on currency	13	0
Ending Balance	$ 384	$ 13