Basis of Presentation and Accounting Policies (Change in Accounting Principle - Consolidated Statements of Cash Flows) (Details) - USD ($) $ in Millions	3 Months Ended			6 Months Ended
	Jun. 30, 2021	Jun. 30, 2020		Jun. 30, 2021	Jun. 30, 2020
Net income	$ 328	$ 118	[1]	$ 678	$ 59	[1]
Provision (benefit) for deferred income taxes				69	(92)
Net periodic defined benefit credit				(41)	(27)
Previously Reported
Net income		113			48
Provision (benefit) for deferred income taxes					(95)
Net periodic defined benefit credit					(13)
Accounting change impact
Net income	4	$ 5		7	11
Provision (benefit) for deferred income taxes	$ 1			2	3
Net periodic defined benefit credit				$ (9)	$ (14)

[1] See Defined Benefit Pension and Other Postretirement Costs in Note 1.