Pension and Other Postretirement Benefits (Funded Status of Pension and Postretirement Benefit Obligations) (Details) - USD ($) $ in Millions	Dec. 31, 2020	Dec. 31, 2019
Defined Benefit Plan Disclosure [Line Items]
Noncurrent liabilities	$ (2,098)	$ (2,121)
Pension benefits [Member]
Defined Benefit Plan Disclosure [Line Items]
Funded status at end of year	(1,815)	(1,787)
Other assets	7	5
Current liabilities	(85)	(69)
Noncurrent liabilities	(1,737)	(1,723)
Net amounts recognized	(1,815)	(1,787)
Pension benefits [Member] | Qualified Plan [Member]
Defined Benefit Plan Disclosure [Line Items]
Funded status at end of year	(712)	(734)
Postretirement benefits [Member]
Defined Benefit Plan Disclosure [Line Items]
Funded status at end of year	(322)	(360)
Other assets	0	0
Current liabilities	(38)	(42)
Noncurrent liabilities	(284)	(318)
Net amounts recognized	$ (322)	$ (360)