Benefit Plans - Pension and postretirement benefits remeasurement gains and losses (Details) - USD ($) $ in Millions	3 Months Ended	6 Months Ended
Jun. 30, 2021	Jun. 30, 2020	Jun. 30, 2021	Jun. 30, 2020
Retirement Benefits [Abstract]
Discount rate	$ 178	$ 433	$ (239)	$ 397
Other assumptions	76	263	(38)	183
Remeasurement of plan assets (gains) losses	(388)	(623)	(167)	(189)
Pension and other postretirement remeasurement (gains) losses	$ (134)	$ 73	$ (444)	$ 391

Amount of gain (loss), recognized immediately as component of net periodic benefit (cost) credit, for change in value of benefit obligation or plan assets from experience different from that assumed, change in actuarial assumption, or consequence of temporarily deviating from substantive plan. Includes, but is not limited to, amount in excess of ten percent of greater of fair value of plan assets or benefit obligation.

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 715
-SubTopic 20
-Section 50
-Paragraph 1
-Subparagraph (h)(4)
-URI http://asc.fasb.org/extlink&oid=123447040&loc=d3e1928-114920

Reference 2: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 715
-SubTopic 20
-Section 50
-Paragraph 6
-Subparagraph (a)(4)
-URI http://asc.fasb.org/extlink&oid=123447040&loc=d3e2709-114920

Reference 3: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 715
-SubTopic 20
-Section 45
-Paragraph 3A
-Subparagraph (b)
-URI http://asc.fasb.org/extlink&oid=123453770&loc=SL108413299-114919

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Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration