Employee Retirement Plans (Postretirement Benefits) (Details) - Postretirement Benefits [Member] - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2019	Dec. 31, 2018
Change in benefit obligation
Benefit obligation at beginning of year	$ 699	$ 789
Service cost	9	10	$ 10
Interest cost	27	24	26
Plan participants’ contributions	8	8
Plan amendments	5	(40)
Actuarial loss (gain)	6	(48)
Other	1
Benefits paid	(50)	(46)
Medicare subsidy received		2
Benefit obligation at end of year	705	699	789
Funded status at end of year
Benefit obligations	$ (705)	$ (789)	$ (789)	$ (705)	$ (699)
Funded status of plans				(705)	(699)
Amounts recognized in the consolidated balance sheets consist of:
Current liability				(34)	(37)
Noncurrent liability				(671)	(662)
Recognized liability				(705)	(699)
Amounts recognized in accumulated other comprehensive income consist of:
Net actuarial loss				28	21
Prior service credit				(32)	(44)
Amount recognized at end of year				$ (4)	$ (23)