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Post-retirement benefits (Tables) | 12 Months Ended
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Dec. 31, 2018
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:
| 2018 |  | 2017
Equities | 20.7% |  |  | 32.4% |
– Quoted |  | 16.7% |  |  | 28.6%
– Private |  | 4.0% |  |  | 3.8%
Bonds | 63.6% |  |  | 53.2% |
– Government fixed income |  | 18.0% |  |  | 14.3%
– Government inflation-linked |  | 15.5% |  |  | 13.1%
– Corporate and other publicly quoted |  | 27.1% |  |  | 23.5%
– Private |  | 3.0% |  |  | 2.3%
Property | 11.0% |  |  | 11.2% |
– Quoted property funds |  | 5.1% |  |  | 5.8%
– Unquoted property funds |  | 5.9% |  |  | 5.4%
Qualifying insurance policies | 0.1% |  |  | 0.2% |
Cash and other | 4.6% |  |  | 3.0% |
Total | 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 |  | 2018 Total % |  | 2017 Total % | 2016 Total %
Proportion relating to current employees | 20% | 15% |  | 19% |  | 20% | 21%
Proportion relating to former employees not yet retired | 11% | 2% |  | 11% |  | 11% | 12%
Proportion relating to retirees | 69% | 83% |  | 70% |  | 69% | 67%
Total | 100% | 100% |  | 100% |  | 100% | 100%
Average duration of obligations (years) | 13.4 | 12.7 |  | 13.4 |  | 13.9 | 14.3
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 |  | 2018 Total % |  | 2017 Total % | 2016 Total %
Canada | 49% | 39% |  | 48% |  | 49% | 46%
UK | 30% | 2% |  | 28% |  | 27% | 27%
US | 11% | 56% |  | 14% |  | 14% | 16%
Switzerland | 5% | 0% |  | 5% |  | 5% | 5%
Other | 5% | 3% |  | 5% |  | 5% | 6%
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 |  | 2018 Total US$m |  | 2017 Total US$m | 2016 Total US$m
Current employer service cost for defined benefit plans | (156) | (9) |  | (165) |  | (155) | (158)
Past service (cost)/income | (34) | (2) |  | (36) |  | 4 | -
Curtailment gains | 2 | - |  | 2 |  | 1 | 5
Settlement gains | 5 | - |  | 5 |  | 1 | -
Net interest on net defined benefit liability | (44) | (35) |  | (79) |  | (79) | (90)
Non-investment expenses paid from the plans | (15) | - |  | (15) |  | (17) | (22)
Total defined benefit expense | (242) | (46) |  | (288) |  | (245) | (265)
Current employer service cost for defined contribution and industry-wide plans | (242) | (2) |  | (244) |  | (255) | (257)
Total expense recognised in the income statement | (484) | (48) |  | (532) |  | (500) | (522)
Summary of total amount recognised in other comprehensive income before tax | Total amount recognised in other comprehensive income before tax
| 2018 US$m | 2017 US$m | 2016 US$m
Actuarial gains/(losses) | 1,382 | (855) | (1,120)
Return on assets (net of interest on assets) | (527) | 894 | 1,031
Gain/(loss) on application of asset ceiling | 52 | (33) | (1)
Total gain/(loss) recognised in other comprehensive income | 907 | 6 | (90)
Summary of amount recognised in balance sheet | The following amounts were measured in accordance with IAS 19 at 31 December:
| Pension benefits | Other benefits |  | 2018 Total US$m |  | 2017 Total US$m
Total fair value of plan assets | 13,203 | - |  | 13,203 |  | 15,257
Present value of obligations – funded | (13,482) | - |  | (13,482) |  | (16,199)
Present value of obligations – unfunded | (401) | (871) |  | (1,272) |  | (1,446)
Present value of obligations – total | (13,883) | (871) |  | (14,754) |  | (17,645)
Effect of asset ceiling | - | - |  | - |  | (111)
Net deficit to be shown in the balance sheet | (680) | (871) |  | (1,551) |  | (2,499)
Comprising: |  |  |  |  |  |
– Deficits | (1,615) | (871) |  | (2,486) |  | (3,370)
– Surpluses | 935 | - |  | 935 |  | 871
Net deficits on pension plans | (680) | - |  | (680) |  | (1,501)
Unfunded post-retirement healthcare obligation | - | (871) |  | (871) |  | (998)
Summary of funding policy and contributions to plans |
| Pension benefits | Other benefits |  | 2018 Total US$m |  | 2017 Total US$m | 2016 Total US$m
Contributions to defined benefit plans | 204 | 44 |  | 248 |  | 404 | 464
Contributions to defined contribution plans | 242 | 2 |  | 244 |  | 243 | 240
Contributions to industry-wide plans | - | - |  | - |  | 12 | 17
Total | 446 | 46 |  | 492 |  | 659 | 721
Summary of movement in net defined benefit liability | Defined contribution plans and industry-wide plans are excluded from the movements below.
| Pension benefits | Other benefits |  | 2018 Total US$m |  | 2017 Total US$m
Change in the net defined benefit liability |  |  |  |  |  |
Net defined benefit liability at the start of the year | (1,501) | (998) |  | (2,499) |  | (2,542)
Amounts recognised in Income statement | (242) | (46) |  | (288) |  | (245)
Amounts recognised in Other comprehensive income | 812 | 95 |  | 907 |  | 6
Employer contributions | 204 | 44 |  | 248 |  | 404
Arrangements divested | (10) | - |  | (10) |  | 13
Currency exchange rate loss | 57 | 34 |  | 91 |  | (135)
Net defined benefit liability at the end of the year | (680) | (871) |  | (1,551) |  | (2,499)
| Pension benefits | Other benefits |  | 2018 Total US$m |  | 2017 Total US$m
Change in present value of obligation |  |  |  |  |  |
Present value of obligation at the start of the year | (16,647) | (998) |  | (17,645) |  | (16,228)
Current employer service costs | (156) | (9) |  | (165) |  | (155)
Past service (cost)/income | (34) | (2) |  | (36) |  | 4
Curtailments | 2 | - |  | 2 |  | 1
Settlements | 299 | - |  | 299 |  | 307
Interest on obligation | (468) | (35) |  | (503) |  | (532)
Contributions by plan participants | (24) | - |  | (24) |  | (23)
Benefits paid | 871 | 44 |  | 915 |  | 949
Experience gains | 11 | 21 |  | 32 |  | 7
Changes in financial assumptions gain/(loss) | 1,276 | 73 |  | 1,349 |  | (718)
Changes in demographic assumptions gain/(loss) | - | 1 |  | 1 |  | (144)
Arrangements divested | 94 | - |  | 94 |  | 13
Currency exchange rate gain/(loss) | 893 | 34 |  | 927 |  | (1,126)
Present value of obligation at the end of the year | (13,883) | (871) |  | (14,754) |  | (17,645)
| Pension benefits | Other benefits |  | 2018 Total US$m |  | 2017 Total US$m
Change in plan assets |  |  |  |  |  |
Fair value of plan assets at the start of the year | 15,257 | - |  | 15,257 |  | 13,749
Settlements | (294) | - |  | (294) |  | (306)
Interest on assets | 434 | - |  | 434 |  | 459
Contributions by plan participants | 24 | - |  | 24 |  | 23
Contributions by employer | 204 | 44 |  | 248 |  | 404
Benefits paid | (871) | (44) |  | (915) |  | (949)
Non-investment expenses | (15) | - |  | (15) |  | (17)
Return on plan assets (net of interest on assets) | (527) | - |  | (527) |  | 894
Arrangements divested | (161) | - |  | (161) |  | -
Currency exchange rate (loss)/gain | (848) | - |  | (848) |  | 1,000
Fair value of plan assets at the end of the year | 13,203 | - |  | 13,203 |  | 15,257
| Pension benefits | Other benefits |  | 2018 Total US$m |  | 2017 Total US$m
Change in the effect of the asset ceiling |  |  |  |  |  |
Effect of the asset ceiling at the start of the year | (111) | - |  | (111) |  | (63)
Interest on the effect of the asset ceiling | (10) | - |  | (10) |  | (6)
Movement in the effect of the asset ceiling | 52 | - |  | 52 |  | (33)
Arrangements divested and other transfers | 57 | - |  | 57 |  | -
Currency exchange rate gain/(loss) | 12 | - |  | 12 |  | (9)
Effect of the asset ceiling at the end of the year | - | - |  | - |  | (111)
Summary of main assumptions rate for valuations of plans and sensitivity analysis | The main assumptions for the valuations of the plans under IAS 19 are set out below.
|  |  | Canada | UK | US | Switzerland
At 31 December 2018 |  |  |  |  |  |
Discount rate |  |  | 3.9% | 2.8% | 4.2% | 0.7%
Inflation (a) |  |  | 1.6% | 3.3% | 2.0% | 1.2%
Rate of increase in pensions |  |  | 0.2% | 2.9% | 0.0% | 0.0%
Rate of increase in salaries |  |  | 2.9% | 3.7% | 3.5% | 2.2%
At 31 December 2017 |  |  |  |  |  |
Discount rate |  |  | 3.4% | 2.3% | 3.5% | 0.5%
Inflation (a) |  |  | 1.8% | 3.2% | 2.1% | 1.2%
Rate of increase in pensions |  |  | 0.5% | 2.8% | 0.0% | 0.4%
Rate of increase in salaries |  |  | 3.1% | 3.6% | 3.6% | 2.2%
(a) | The inflation assumption shown for the UK is for the Retail Price Index. The assumption for the Consumer Price Index at 31 December 2018 was 2.2% (2017: 2.1%).
The results of this sensitivity analysis are summarised in the table below.
|  | 2018 | 2017
|  | Approximate (increase)/decrease in obligations | Approximate (increase)/decrease in obligations
Assumption | Change in assumption | Pensions US$m | Other US$m | Pensions US$m | Other US$m
Discount rate | Increase of 0.5 percentage points | 782 | 51 | 1,091 | 59
| Decrease of 0.5 percentage points | (832) | (55) | (1,169) | (63)
Inflation | Increase of 0.5 percentage points | (389) | (17) | (579) | (20)
| Decrease of 0.5 percentage points | 369 | 15 | 550 | 18
Salary increases | Increase of 0.5 percentage points | (46) | (1) | (74) | (1)
| Decrease of 0.5 percentage points | 45 | 1 | 72 | 1
Demographic – allowance for future improvements in longevity | Participants assumed to have the mortality rates of individuals who are one year older | 381 | 18 | 509 | 20
| Participants assumed to have the mortality rates of individuals who are one year younger | (381) | (18) | (509) | (20)

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- Definition The disclosure of information about the maturity profile of a defined benefit obligation. This will include the weighted average duration of the defined benefit obligation and may include other information about the distribution of the timing of benefit payments, such as a maturity analysis of the benefit payments. [Refer: Defined benefit obligation, at present value] + References Reference 1: http://www.xbrl.org/2003/role/disclosureRef -Name IAS -Number 19 -IssueDate 2017-01-01 -Paragraph 147 -Subparagraph c -URI http://eifrs.ifrs.org/eifrs/XBRL?type=IAS&num=19&date=2017-03-01&anchor=para_147_c&doctype=Standard -URIDate 2017-03-09 + Details
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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 2017-01-01 -Paragraph 145 -URI http://eifrs.ifrs.org/eifrs/XBRL?type=IAS&num=19&date=2017-03-01&anchor=para_145&doctype=Standard -URIDate 2017-03-09 + Details
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