Retirement benefits - Financial Assumptions (Details) - year	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
U.K.
Disclosure of defined benefit plans [line items]
Discount rate	2.40%	2.60%	3.70%
Retail Price Inflation	3.10%	3.20%	3.00%
Salary inflation			4.00%
Consumer Price Inflation	2.10%	2.20%	2.00%
Pension increases	1.70%	1.80%	1.70%
U.K. \| Pre 6 April 1997
Disclosure of defined benefit plans [line items]
Pension increases	1.90%	2.00%	1.80%
U.K. \| 1997 - 2005
Disclosure of defined benefit plans [line items]
Pension increases	2.10%	2.20%	2.10%
Non-U.K.
Disclosure of defined benefit plans [line items]
Discount rate	3.60%	4.20%	4.50%
Male \| U.K. \| Age 65 at accounting date
Disclosure of defined benefit plans [line items]
Life expectancy	21.6	21.5
Male \| U.K. \| Aged 65 at 20 years after accounting date
Disclosure of defined benefit plans [line items]
Life expectancy	23.3	23.2
Female \| U.K. \| Age 65 at accounting date
Disclosure of defined benefit plans [line items]
Life expectancy	24.6	24.5
Female \| U.K. \| Aged 65 at 20 years after accounting date
Disclosure of defined benefit plans [line items]
Life expectancy	26.5	26.4

The discount rate used as the significant actuarial assumption to determine the present value of a defined benefit obligation. [Refer: Defined benefit obligation, at present value; Actuarial assumptions [member]]

Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef
-Name IAS
-Number 19
-IssueDate 2017-01-01
-Paragraph 144
-URI http://eifrs.ifrs.org/eifrs/XBRL?type=IAS&num=19&date=2017-03-01&anchor=para_144&doctype=Standard
-URIDate 2017-03-09

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- Definition

The expected rate of inflation that is used as a significant actuarial assumption to determine the present value of a defined benefit obligation. [Refer: Defined benefit plans [member]; Defined benefit obligation, at present value; Actuarial assumptions [member]]

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The expected rate of increases in pension that is used as a significant actuarial assumption to determine the present value of a defined benefit obligation. [Refer: Defined benefit plans [member]; Defined benefit obligation, at present value; Actuarial assumptions [member]]

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The expected rate of salary increases used as a significant actuarial assumption to determine the present value of a defined benefit obligation. [Refer: Defined benefit plans [member]; Defined benefit obligation, at present value; Actuarial assumptions [member]]

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The life expectancy after retirement used as a significant actuarial assumption to determine the present value of a defined benefit obligation. [Refer: Defined benefit obligation, at present value; Actuarial assumptions [member]]

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Actuarial Assumption Of Expected Rates Of Retail Price Inflation

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