Retirement Plans (Reconciliation of The Change In AOCL For Defined-Benefit Retirement Plans) (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019		Dec. 31, 2018	[1]
Amortization of:
Change in AOCL, pretax	$ 453	$ 857	[1]	$ 45
Pension Benefits
Compensation And Retirement Disclosure Line Items
Net actuarial loss (gain)	863	1,151
Prior service credit (cost)	(38)	3
Amortization of:
Net actuarial (loss) gain from prior years	(387)	(355)
Prior service credit	18	19
Change in AOCL, pretax	456	818
Other  Post-retirement Benefits
Compensation And Retirement Disclosure Line Items
Net actuarial loss (gain)	(6)	20
Prior service credit (cost)	(1)	8
Amortization of:
Net actuarial (loss) gain from prior years	3	8
Prior service credit	1	3
Change in AOCL, pretax	$ (3)	$ 39

[1] *Prior-period information has been restated for the retrospective application of a change in accounting principle related to the amortization of actuarial gains and losses for our qualified U.S. government pension plans, which we adopted in the fourth quarter of 2020. For further discussion of this change in accounting principle, see Note T to the Consolidated Financial Statements.