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Income Taxes Operating Loss Carryforwards (Details) - USD ($) $ in Millions | Dec. 31, 2020 | Dec. 31, 2019
--- | --- | ---
U.K. |  |
Operating Loss Carryforwards [Line Items] |  |
Operating loss carryforwards | $ 266 | $ 438
Capital loss carryforwards | 577 | 411
Interest carryforwards | 121 | 203
U.S. Federal |  |
Operating Loss Carryforwards [Line Items] |  |
Operating loss carryforwards | 49 | 1
Capital loss carryforwards | 112 | 112
Interest carryforwards | 1,220 | 355
U.S. State |  |
Operating Loss Carryforwards [Line Items] |  |
Operating loss carryforwards | 378 | 376
Capital loss carryforwards | 123 | 123
Interest carryforwards | 573 | 172
Other |  |
Operating Loss Carryforwards [Line Items] |  |
Operating loss carryforwards | 400 | 308
Capital loss carryforwards | 42 | 29
Interest carryforwards | $ 34 | $ 159

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- Definition Amount of operating loss carryforward, before tax effects, available to reduce future taxable income under enacted tax laws. + References Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 740 -SubTopic 10 -Section 50 -Paragraph 3 -Subparagraph (a) -URI http://asc.fasb.org/extlink&oid=84230637&loc=d3e32559-109319 + Details
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