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Income Taxes - Income from continuing operations before income tax (Details) - USD ($) $ in Millions | 12 Months Ended
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Dec. 31, 2017 | Dec. 31, 2016 | Dec. 31, 2015
Income before income taxes: |  |  |
Income from continuing operations before income taxes | $ 685 | $ 1,401 | $ 1,428
Current: |  |  |
Total current | 268 | 248 | 341
Deferred tax expense (benefit): |  |  |
Total deferred | (18) | (100) | (166)
Total income taxes expenses | 250 | 148 | 175
U.K. |  |  |
Income before income taxes: |  |  |
Income from continuing operations before income taxes | (420) | (201) | 144
Current: |  |  |
Total current | 1 | (54) | 42
Deferred tax expense (benefit): |  |  |
Total deferred | (5) | 59 | (39)
U.S. federal |  |  |
Income before income taxes: |  |  |
Income from continuing operations before income taxes | (765) | (329) | (283)
Current: |  |  |
Total current | 48 | 88 | 22
Deferred tax expense (benefit): |  |  |
Total deferred | 12 | (110) | (94)
U.S. state and local |  |  |
Current: |  |  |
Total current | 18 | 7 | 32
Deferred tax expense (benefit): |  |  |
Total deferred | (35) | (9) | (4)
Other |  |  |
Income before income taxes: |  |  |
Income from continuing operations before income taxes | 1,870 | 1,931 | 1,567
Current: |  |  |
Total current | 201 | 207 | 245
Deferred tax expense (benefit): |  |  |
Total deferred | $ 10 | $ (40) | $ (29)

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