Report Of The Directors Strategic Report - Adjusted Balance Sheet Reconciliation (Details) - USD ($) $ in Millions	Jun. 30, 2018	Jan. 01, 2018	[1]	Dec. 31, 2017	Jun. 30, 2017
Consolidation Items [Line Items]
Loans and advances to customers (net)	$ 973,443	$ 949,737		$ 962,964
Interests in associates and joint ventures	22,572	21,802		22,744
Total external assets	2,607,314	2,518,430		2,521,771
Customer accounts	1,356,307	$ 1,360,227		1,364,462
Adjusted
Consolidation Items [Line Items]
Loans and advances to customers (net)	973,443			943,545	$ 919,141
Interests in associates and joint ventures	22,572			22,484	21,307
Total external assets				2,477,799	2,496,050
Customer accounts	$ 1,356,307			1,339,663	$ 1,311,383
Currency translation
Consolidation Items [Line Items]
Loans and advances to customers (net)				19,419
Interests in associates and joint ventures				260
Total external assets				43,972
Customer accounts				$ 24,799

[1] 9Balances at 1 January 2018 have been prepared in accordance with accounting policies referred to on page 84. 31 December 2017 balances have not been re-presented.