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Lease Commitments - Cash Flow of Lessee (Details) - USD ($) $ in Millions | 12 Months Ended
--- | ---
Dec. 31, 2020 | Dec. 31, 2019
Cash paid for amounts included in the measurement of lease liabilities |  |
Operating cash flows for operating leases | $ 236 | $ 264
Financing cash flows for finance leases | 12 | 17
Non-cash related activities |  |
ROU assets obtained in exchange for new operating lease liabilities | 146 | 155
ROU assets obtained in exchange for new finance lease liabilities | 13 | 48
Operating lease ROU asset expense | 178 | 195
Changes in Non-current operating lease liabilities | $ (47) | $ (70)

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- Definition Amount of cash outflow for principal payment on finance lease. + References Reference 1: http://www.xbrl.org/2003/role/disclosureRef -Publisher FASB -Name Accounting Standards Codification -Topic 842 -SubTopic 20 -Section 45 -Paragraph 5 -Subparagraph (a) -URI http://asc.fasb.org/extlink&oid=121603541&loc=SL77918643-209977 Reference 2: http://www.xbrl.org/2003/role/disclosureRef -Publisher FASB -Name Accounting Standards Codification -Topic 842 -SubTopic 20 -Section 50 -Paragraph 4 -Subparagraph (g)(1) -URI http://asc.fasb.org/extlink&oid=121609121&loc=SL77918686-209980 + Details
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