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Employee Benefits (Details) £ in Millions, $ in Millions | 3 Months Ended | 9 Months Ended | 12 Months Ended
--- | --- | --- | ---
Sep. 30, 2018 GBP (£) | Sep. 30, 2018 USD ($) | Sep. 30, 2017 USD ($) | Sep. 30, 2018 GBP (£) | Sep. 30, 2018 USD ($) | Sep. 30, 2017 USD ($) | Dec. 31, 2017
Defined Benefit Plan Disclosure |  |  |  |  |  |  |
Federal statutory income tax rate |  |  |  |  |  |  | 35.00%
U.K. |  |  |  |  |  |  |
Defined Benefit Plan Disclosure |  |  |  |  |  |  |
Service cost |  | $ 0 | $ 0 |  | $ 0 | $ 0 |
Interest cost |  | 26 | 31 |  | 84 | 91 |
Expected return on plan assets, net of administration expenses |  | (46) | (50) |  | (147) | (147) |
Amortization of prior-service cost |  | 1 | 0 |  | 1 | 0 |
Amortization of net actuarial loss |  | 6 | 8 |  | 21 | 23 |
Net periodic (benefit) cost |  | (13) | (11) |  | (41) | (33) |
Loss on pension settlement |  | 9 | 0 |  | 32 | 0 |
Total net periodic (benefit) cost |  | (4) | (11) |  | (9) | (33) |
Payment for settlement |  |  |  | £ 125 | 164 |  |
Benefit obligation period increase (decrease) | £ (108) | (143) |  |  |  |  |
Benefit obligation, (increase) decrease for settlement | £ 7 | 9 |  | £ 24 | 32 |  |
Expected employer contributions current fiscal year |  | 92 |  |  | 92 |  |
Contributions made to defined benefit pension plans |  | 27 | 22 |  | 75 | 64 |
U.S. |  |  |  |  |  |  |
Defined Benefit Plan Disclosure |  |  |  |  |  |  |
Service cost |  | 0 | 0 |  | 0 | 0 |
Interest cost |  | 24 | 24 |  | 74 | 72 |
Expected return on plan assets, net of administration expenses |  | (36) | (34) |  | (108) | (104) |
Amortization of prior-service cost |  | 0 | 0 |  | 1 | 1 |
Amortization of net actuarial loss |  | 15 | 13 |  | 45 | 38 |
Net periodic (benefit) cost |  | 3 | 3 |  | 12 | 7 |
Loss on pension settlement |  | 0 | 0 |  | 0 | 0 |
Total net periodic (benefit) cost |  | 3 | 3 |  | 12 | 7 |
Expected employer contributions current fiscal year |  | 143 |  |  | 143 |  |
Contributions to defined benefit pension plans for the current fiscal year at 35% Federal tax rate |  | 100 |  |  |  |  |
Contributions made to defined benefit pension plans |  | 108 | 5 |  | 133 | 31 |
Other |  |  |  |  |  |  |
Defined Benefit Plan Disclosure |  |  |  |  |  |  |
Service cost |  | 0 | 0 |  | 0 | 0 |
Interest cost |  | 6 | 7 |  | 20 | 19 |
Expected return on plan assets, net of administration expenses |  | (11) | (13) |  | (34) | (35) |
Amortization of prior-service cost |  | 0 | 0 |  | 0 | 0 |
Amortization of net actuarial loss |  | 3 | 3 |  | 9 | 9 |
Net periodic (benefit) cost |  | (2) | (3) |  | (5) | (7) |
Loss on pension settlement |  | 0 | 0 |  | 0 | 0 |
Total net periodic (benefit) cost |  | (2) | (3) |  | (5) | (7) |
Expected employer contributions current fiscal year |  | 22 |  |  | 22 |  |
Contributions made to defined benefit pension plans |  | $ 3 | $ 3 |  | $ 14 | $ 14 |

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