Lease Obligations - Lessee - Undiscounted Cash Flows (Details) - USD ($) $ in Millions	Dec. 31, 2020	Dec. 31, 2019
Operating Leases
2021	$ 86
2022	81
2023	74
2024	65
2025	58
Thereafter	246
Total undiscounted cash flows	610
Less: Difference between undiscounted cash flows and discounted cash flows	83
Present value of lease liabilities	527	$ 555
Finance Leases
2021	18
2022	19
2023	16
2024	17
2025	10
Thereafter	78
Total undiscounted cash flows	158
Less: Difference between undiscounted cash flows and discounted cash flows	28
Present value of lease liabilities	130	$ 35
Total
2021	104
2022	100
2023	90
2024	82
2025	68
Thereafter	324
Total undiscounted cash flows	768
Less: Difference between undiscounted cash flows and discounted cash flows	111
Present value of lease liabilities	$ 657

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Lease liability payments due year five.

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Lease liability payments due year four.

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Lease liability payments due year three.

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LeaseLiabilityUndiscountedExcessAmount.

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Present value of lessee's discounted obligation for lease payments from finance lease.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 842
-SubTopic 20
-Section 50
-Paragraph 6
-URI http://asc.fasb.org/extlink&oid=121609121&loc=SL77918701-209980

Reference 2: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 842
-SubTopic 20
-Section 45
-Paragraph 1
-Subparagraph (b)
-URI http://asc.fasb.org/extlink&oid=121603541&loc=SL77918627-209977

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Amount of lessee's undiscounted obligation for lease payments for finance lease.

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Amount of lessee's undiscounted obligation for lease payment for finance lease to be paid after fifth fiscal year following current fiscal year. Excludes interim and annual periods when interim periods are reported from current statement of financial position date (rolling approach).

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Amount of lessee's undiscounted obligation for lease payment for operating lease.

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Amount of lessee's undiscounted obligation for lease payment for operating lease due after fifth fiscal year following current fiscal year. Excludes interim and annual periods when interim periods are reported from current statement of financial position date (rolling approach).

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Present value of lessee's discounted obligation for lease payments from operating lease.

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-Publisher FASB
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-Paragraph 1
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-URI http://asc.fasb.org/extlink&oid=121603541&loc=SL77918627-209977

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