Other Equity - Additional disclosures (Details) - GBP (£) £ / shares in Units, £ in Millions, shares in Millions	12 Months Ended
Dec. 31, 2017	Dec. 31, 2015	Dec. 31, 2016
Merger reserve
Transfer (to) from retained earnings - merger reserve	£ 0	£ (2,341)
Share awards and options \| Own shares held
Own shares held	16		39
Par value	£ 1
Own shares acquired	30
Delivery of own shares held	53

The nominal value per share.

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
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+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
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The transfer to or from of merger reserve to retained earnings.

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The number of shares in the entity sold or issued by the entity or by its subsidiaries or associates.

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