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Post-retirement benefits (Tables) | 12 Months Ended
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Dec. 31, 2017
Disclosure Of Pension And Post Retirement Healthcare Plans [Abstract] |
Summary of fair value of plan assets | The proportions of the total fair value of assets in the pension plans for each asset class at the balance sheet date were:
| 2017 |  | 2016
Equities | 32.4% |  |  | 36.8% |
– Quoted |  | 28.6% |  |  | 32.5%
– Private |  | 3.8% |  |  | 4.3%
Bonds | 53.2% |  |  | 47.9% |
– Government fixed income |  | 14.3% |  |  | 11.3%
– Government inflation-linked |  | 13.1% |  |  | 12.0%
– Corporate and other publicly quoted |  | 23.5% |  |  | 22.3%
– Private |  | 2.3% |  |  | 2.3%
Property | 11.2% |  |  | 11.0% |
– Quoted property funds |  | 5.8% |  |  | 5.8%
– Unquoted property funds |  | 5.4% |  |  | 5.2%
Qualifying insurance policies | 0.2% |  |  | 0.6% |
Cash & other | 3.0% |  |  | 3.7% |
| 100.0% |  |  | 100.0% |
Summary of maturity of defined benefit obligations | An approximate analysis of the maturity of the obligations is given in the table below:
| Pension benefits | Other benefits |  | 2017 Total % |  | 2016 Total % | 2015 Total %
Proportion relating to current employees | 20% | 16% |  | 20% |  | 21% | 22%
Proportion relating to former employees not yet retired | 12% | 1% |  | 11% |  | 12% | 11%
Proportion relating to retirees | 68% | 83% |  | 69% |  | 67% | 67%
Total | 100% | 100% |  | 100% |  | 100% | 100%
Average duration of obligations (years) | 14.0 | 12.7 |  | 13.9 |  | 14.3 | 13.4
Summary of geographical distribution of defined benefit obligations | An approximate analysis of the geographic distribution of the obligations is given in the table below:
| Pension benefits | Other benefits |  | 2017 Total % |  | 2016 Total % | 2015 Total %
Canada | 49% | 41% |  | 49% |  | 46% | 44%
UK | 29% | 2% |  | 27% |  | 27% | 29%
US | 12% | 54% |  | 14% |  | 16% | 15%
Switzerland | 5% | 0% |  | 5% |  | 5% | 6%
Eurozone | 3% | 0% |  | 3% |  | 4% | 4%
Other | 2% | 3% |  | 2% |  | 2% | 2%
Total | 100% | 100% |  | 100% |  | 100% | 100%
Summary of total expense recognised in the income statement | Total expense recognised in the income statement
| Pension benefits | Other benefits |  | 2017 Total % |  | 2016 Total US$m | 2015 Total US$m
Current employer service cost for defined benefit plans | (146) | (9) |  | (155) |  | (158) | (184)
Past service income | 1 | 3 |  | 4 |  | - | 144
Curtailment gains | 1 | - |  | 1 |  | 5 | 13
Settlement gains | 1 | - |  | 1 |  | - | 11
Net interest on net defined benefit liability | (45) | (34) |  | (79) |  | (90) | (113)
Non-investment expenses paid from the plans | (17) | - |  | (17) |  | (22) | (21)
Total defined benefit expense | (205) | (40) |  | (245) |  | (265) | (150)
Current employer service cost for defined contribution and industry-wide plans | (253) | (2) |  | (255) |  | (257) | (289)
Total expense recognised in the income statement | (458) | (42) |  | (500) |  | (522) | (439)
Summary of total amount recognised in other comprehensive income before tax | Total amount recognised in other comprehensive income before tax
| 2017 US$m | 2016 US$m | 2015 US$m
Actuarial (losses)/gains | (855) | (1,120) | 548
Return on assets (net of interest on assets) | 894 | 1,031 | 79
Loss on application of asset ceiling | (33) | (1) | (8)
Total gain/(loss) recognised in other comprehensive income | 6 | (90) | 619
Summary of amount recognised in balance sheet | The following amounts were measured in accordance with IAS 19 at 31 December:
| Pension benefits | Other benefits |  | 2017 Total US$m |  | 2016 Total US$m
Total fair value of plan assets | 15,257 | - |  | 15,257 |  | 13,749
Present value of obligations – funded | (16,199) | - |  | (16,199) |  | (14,504)
Present value of obligations – unfunded | (448) | (998) |  | (1,446) |  | (1,724)
Present value of obligations – total | (16,647) | (998) |  | (17,645) |  | (16,228)
Effect of asset ceiling | (111) | - |  | (111) |  | (63)
Net deficit to be shown in the balance sheet | (1,501) | (998) |  | (2,499) |  | (2,542)
Comprising: |  |  |  |  |  |
– Deficits | (2,372) | (998) |  | (3,370) |  | (3,167)
– Surpluses | 871 | - |  | 871 |  | 625
Net deficits on pension plans | (1,501) | - |  | (1,501) |  | (1,616)
Unfunded post-retirement healthcare obligation | - | (998) |  | (998) |  | (926)
Summary of funding policy and contributions to plans |
| Pension benefits | Other benefits |  | 2017 Total US$m |  | 2016 Total US$m | 2015 Total US$m
Contributions to defined benefit plans | 349 | 55 |  | 404 |  | 464 | 328
Contributions to defined contribution plans | 241 | 2 |  | 243 |  | 240 | 272
Contributions to industry-wide plans | 12 | - |  | 12 |  | 17 | 17
Total | 602 | 57 |  | 659 |  | 721 | 617
Summary of movement in net defined benefit liability | Defined contribution plans and industry-wide plans are excluded from the movements below.
| Pension benefits | Other benefits |  | 2017 Total US$m |  | 2016 Total US$m
Change in the net defined benefit liability |  |  |  |  |  |
Net defined benefit liability at the start of the year | (1,616) | (926) |  | (2,542) |  | (2,530)
Amounts recognised in Income | (205) | (40) |  | (245) |  | (265)
Amounts recognised in Other comprehensive income | 62 | (56) |  | 6 |  | (90)
Employer contributions | 349 | 55 |  | 404 |  | 464
Arrangements divested | 13 | - |  | 13 |  | (8)
Currency exchange rate loss | (104) | (31) |  | (135) |  | (113)
Net defined benefit liability at the end of the year | (1,501) | (998) |  | (2,499) |  | (2,542)
| Pension benefits | Other benefits |  | 2017 Total US$m |  | 2016 Total US$m
Change in present value of obligation |  |  |  |  |  |
Present value of obligation at the start of the year | (15,302) | (926) |  | (16,228) |  | (16,123)
Current employer service costs | (146) | (9) |  | (155) |  | (158)
Past service income | 1 | 3 |  | 4 |  | -
Curtailments | 1 | - |  | 1 |  | 5
Settlements | 307 | - |  | 307 |  | -
Interest on obligation | (498) | (34) |  | (532) |  | (577)
Contributions by plan participants | (23) | - |  | (23) |  | (23)
Benefits paid | 894 | 55 |  | 949 |  | 967
Experience (loss)/gain | (2) | 9 |  | 7 |  | 139
Changes in financial assumptions loss | (678) | (40) |  | (718) |  | (1,187)
Changes in demographic assumptions loss | (119) | (25) |  | (144) |  | (72)
Arrangements divested | 13 | - |  | 13 |  | 86
Currency exchange rate (loss)/gain | (1,095) | (31) |  | (1,126) |  | 715
Present value of obligation at the end of the year | (16,647) | (998) |  | (17,645) |  | (16,228)
| Pension benefits | Other benefits |  | 2017 Total US$m |  | 2016 Total US$m
Change in plan assets |  |  |  |  |  |
Fair value of plan assets at the start of the year | 13,749 | - |  | 13,749 |  | 13,642
Settlements | (306) | - |  | (306) |  | -
Interest on assets | 459 | - |  | 459 |  | 492
Contributions by plan participants | 23 | - |  | 23 |  | 23
Contributions by employer | 349 | 55 |  | 404 |  | 464
Benefits paid | (894) | (55) |  | (949) |  | (967)
Non-investment expenses | (17) | - |  | (17) |  | (22)
Return on plan assets (net of interest on assets) | 894 | - |  | 894 |  | 1,031
Arrangements divested | - | - |  | - |  | (94)
Currency exchange rate gain/(loss) | 1,000 | - |  | 1,000 |  | (820)
Fair value of plan assets at the end of the year | 15,257 | - |  | 15,257 |  | 13,749
| Pension benefits | Other benefits |  | 2017 Total US$m |  | 2016 Total US$m
Change in the effect of the asset ceiling |  |  |  |  |  |
Effect of the asset ceiling at the start of the year | (63) | - |  | (63) |  | (49)
Interest on the effect of the asset ceiling | (6) | - |  | (6) |  | (5)
Movement in the effect of the asset ceiling | (33) | - |  | (33) |  | (1)
Currency exchange rate loss | (9) | - |  | (9) |  | (8)
Effect of the asset ceiling at the end of the year | (111) | - |  | (111) |  | (63)
Summary of main assumptions rate for valuations of plans and sensitivity analysis | The main assumptions for the valuations of the plans under IAS 19 are set out below.
|  |  | Canada | UK | US | Switzerland | Eurozone
At 31 December 2017 |  |  |  |  |  |  |
Discount rate |  |  | 3.4% | 2.3% | 3.5% | 0.5% | 1.5%
Inflation (a) |  |  | 1.8% | 3.2% | 2.1% | 1.2% | 1.7%
Rate of increase in pensions |  |  | 0.5% | 2.8% | 0.0% | 0.4% | 1.7%
Rate of increase in salaries |  |  | 3.1% | 3.6% | 3.6% | 2.2% | 1.9%
At 31 December 2016 |  |  |  |  |  |  |
Discount rate |  |  | 3.8% | 2.6% | 3.9% | 0.6% | 1.4%
Inflation (a) |  |  | 1.9% | 3.3% | 2.1% | 1.0% | 1.6%
Rate of increase in pensions |  |  | 0.4% | 2.9% | 0.0% | 0.0% | 1.4%
Rate of increase in salaries |  |  | 3.2% | 3.7% | 3.6% | 2.0% | 2.4%
(a) | The inflation assumption shown for the UK is for the Retail Price Index. The assumption for the Consumer Price Index at 31 December 2017 was 2.1 per cent (2016: 2.2 per cent).
The results of this sensitivity analysis are summarised in the table below.
|  | 2017 | 2016
|  | Approximate (increase)/decrease in obligations | Approximate (increase)/decrease in obligations
Assumption | Change in assumption | Pensions US$m | Other US$m | Pensions US$m | Other US$m
Discount rate | Increase of 0.5 percentage points | 1,091 | 59 | 1,031 | 57
| Decrease of 0.5 percentage points | (1,169) | (63) | (1,107) | (61)
Inflation | Increase of 0.5 percentage points | (579) | (20) | (536) | (19)
| Decrease of 0.5 percentage points | 550 | 18 | 507 | 17
Salary increases | Increase of 0.5 percentage points | (74) | (1) | (77) | (3)
| Decrease of 0.5 percentage points | 72 | 1 | 75 | 2
Demographic – allowance for future improvements in longevity | Participants assumed to have the mortality rates of individuals who are one year older | 509 | 20 | 481 | 20
| Participants assumed to have the mortality rates of individuals who are one year younger | (509) | (20) | (481) | (20)
Medical costs trend rates | Increase of 1.0 percentage points | - | (38) | - | (37)
| Decrease of 1.0 percentage points | - | 33 | - | 31

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- Definition The disclosure of a sensitivity analysis for significant actuarial assumptions used to determine the present value of a defined benefit obligation. [Refer: Actuarial assumptions [member]; Defined benefit obligation, at present value] + References Reference 1: http://www.xbrl.org/2003/role/disclosureRef -Name IAS -Number 19 -IssueDate 2016-01-13 -Paragraph 145 -URI http://eifrs.ifrs.org/eifrs/XBRL?type=IAS&num=19&date=2016-03-30&anchor=para_145&doctype=Standard -URIDate 2016-03-31 + Details
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