Retirement Plans (Schedule of ABO That Exceeded Plan Assets) (Details) - USD ($) $ in Millions	Dec. 31, 2019	Dec. 31, 2018
Compensation And Retirement Disclosure Line Items
PBO	$ (17,651)	$ (15,354)
Pension Benefits
Compensation And Retirement Disclosure Line Items
ABO	(17,080)	(14,856)
Fair value of plan assets	12,354	10,832
Other Post-retirement Benefits
Compensation And Retirement Disclosure Line Items
ABO	(783)	(709)
Fair value of plan assets	$ 301	$ 264

Amount of accumulated benefit obligation for defined benefit plan with accumulated benefit obligation in excess of plan assets.

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 715
-SubTopic 20
-Section 50
-Paragraph 3
-Subparagraph (a)
-URI http://asc.fasb.org/extlink&oid=118255775&loc=d3e2417-114920

Reference 2: http://www.xbrl.org/2003/role/exampleRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 715
-SubTopic 20
-Section 55
-Paragraph 17
-URI http://asc.fasb.org/extlink&oid=118257860&loc=d3e4179-114921

Reference 3: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 715
-SubTopic 20
-Section 50
-Paragraph 3
-Subparagraph (b)
-URI http://asc.fasb.org/extlink&oid=118255775&loc=d3e2417-114920

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