Basis of Presentation and Accounting Policies (Change in Accounting Principle - Consolidated Balance Sheets)(Details) - USD ($) $ in Millions	Jun. 30, 2021		Dec. 31, 2020	Jun. 30, 2020	[1]
Accumulated other comprehensive (loss) income	$ (120)	[1]	$ 64	$ 66
Retained earnings	10,202		9,727
Accounting change impact
Accumulated other comprehensive (loss) income	(7)		(104)
Retained earnings	$ 7		104
Previously Reported
Accumulated other comprehensive (loss) income			168
Retained earnings			$ 9,623

[1] Balances at beginning of period, net of tax, and changes for the six months ended June 30, 2021 have been recast to reflect the retrospective application of the Corporation's election to change the accounting method for certain components of the qualified defined benefit pension plan as of January 1, 2021. Refer to Note 1 for further information.