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Employee Benefits (Details) £ in Millions, $ in Millions | 3 Months Ended | 6 Months Ended | 12 Months Ended |
--- | --- | --- | --- | ---
Jun. 30, 2018 GBP (£) | Jun. 30, 2018 USD ($) | Jun. 30, 2017 USD ($) | Jun. 30, 2018 GBP (£) | Jun. 30, 2018 USD ($) | Jun. 30, 2017 USD ($) | Dec. 31, 2017 | Sep. 30, 2018 USD ($)
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 |  | 29 | 30 |  | 58 | 60 |  |
Expected return on plan assets, net of administration expenses |  | (50) | (49) |  | (101) | (97) |  |
Amortization of prior-service cost |  | 0 | 0 |  | 0 | 0 |  |
Amortization of net actuarial loss |  | 7 | 8 |  | 15 | 15 |  |
Net periodic cost (benefit) |  | (14) | (11) |  | (28) | (22) |  |
Loss on pension settlement |  | 16 | 0 |  | 23 | 0 |  |
Total net periodic cost (benefit) |  | 2 | (11) |  | (5) | (22) |  |
Payment for settlement |  |  |  | £ 99 | 132 |  |  |
Benefit obligation period increase (decrease) | £ (87) | (115) |  |  |  |  |  |
Benefit obligation, (increase) decrease for settlement | £ 12 | 16 |  | £ 17 | 23 |  |  |
Estimate of contributions to defined benefit pension plans for the current fiscal year |  | 92 |  |  | 92 |  |  |
Contributions made to defined benefit pension plans |  | 25 | 26 |  | 48 | 42 |  |
U.S. |  |  |  |  |  |  |  |
Defined Benefit Plan Disclosure |  |  |  |  |  |  |  |
Service cost |  | 0 | 0 |  | 0 | 0 |  |
Interest cost |  | 25 | 24 |  | 50 | 48 |  |
Expected return on plan assets, net of administration expenses |  | (36) | (35) |  | (72) | (70) |  |
Amortization of prior-service cost |  | 1 | 1 |  | 1 | 1 |  |
Amortization of net actuarial loss |  | 15 | 12 |  | 30 | 25 |  |
Net periodic cost (benefit) |  | 5 | 2 |  | 9 | 4 |  |
Loss on pension settlement |  | 0 | 0 |  | 0 | 0 |  |
Total net periodic cost (benefit) |  | 5 | 2 |  | 9 | 4 |  |
Estimate of contributions to defined benefit pension plans for the current fiscal year |  | 143 |  |  | 143 |  |  |
Contributions made to defined benefit pension plans |  | 8 | 13 |  | 25 | 26 |  |
Other |  |  |  |  |  |  |  |
Defined Benefit Plan Disclosure |  |  |  |  |  |  |  |
Service cost |  | 0 | 0 |  | 0 | 0 |  |
Interest cost |  | 7 | 6 |  | 14 | 12 |  |
Expected return on plan assets, net of administration expenses |  | (11) | (11) |  | (23) | (22) |  |
Amortization of prior-service cost |  | 0 | 0 |  | 0 | 0 |  |
Amortization of net actuarial loss |  | 3 | 3 |  | 6 | 6 |  |
Net periodic cost (benefit) |  | (1) | (2) |  | (3) | (4) |  |
Loss on pension settlement |  | 0 | 0 |  | 0 | 0 |  |
Total net periodic cost (benefit) |  | (1) | (2) |  | (3) | (4) |  |
Estimate of contributions to defined benefit pension plans for the current fiscal year |  | 22 |  |  | 22 |  |  |
Contributions made to defined benefit pension plans |  | $ 3 | $ 9 |  | $ 11 | $ 11 |  |
Scenario, Forecast | U.S. |  |  |  |  |  |  |  |
Defined Benefit Plan Disclosure |  |  |  |  |  |  |  |
Estimate of contributions to defined benefit pension plans for the current fiscal year |  |  |  |  |  |  |  | $ 100

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