Business Segments - Summary on Reconciliation of Results Under Ifrs to Us Gaap (Detail) - USD ($) $ in Millions		3 Months Ended			6 Months Ended
		Jun. 30, 2020		Jun. 30, 2019	Jun. 30, 2020		Jun. 30, 2019	Dec. 31, 2019
Operating Statistics [Line Items]
Net Interest Income		$ 516		$ 610	$ 1,035		$ 1,234
Group Reporting Basis Other operating income		499		365	870		703
Group Reporting Basis Total operating income		1,015		975	1,905		1,937
Expected credit losses / provision for credit losses		236			615
Expected credit losses/provision for credit losses				25			35
Group Reporting Basis Revenues		779		950	1,290		1,902
Operating Expenses		732		761	2,241		1,509
Group Reporting Basis Profit (Loss) Before Income Tax		47		189	(951)		393
Total Assets		260,376		215,763	260,376		215,763
Group Reporting Basis Total loans, net		69,857		70,328	69,857		70,328
Group Reporting Basis Goodwill		358		1,260	358		1,260
Group Reporting Basis Total deposits		143,530		100,081	143,530		100,081
Net interest income		538		540	1,042		1,102
Other operating income	[1]	464		436	851		826
Total operating income		1,002		976	1,893		1,928
Provision for credit losses		219			945
Provision for credit losses		337		46	849		104
Total income		783		930	948		1,824
Operating expenses		727		774	2,332		1,524
Income (loss) before income tax		56		156	(1,384)		300
Total assets		212,862	[2]	184,063	212,862	[2]	184,063	$ 175,375	[2]
Total loans, net		71,276		71,865	71,276		71,865	67,916
Goodwill		458		1,607	458		1,607	1,242
Total deposits		156,033		116,961	156,033		116,961	$ 119,693
Group Reporting Basis Adjustments [Member]
Operating Statistics [Line Items]
Net Interest Income	[3]	2		3	5		9
Group Reporting Basis Other operating income	[3]	(19)		(3)	(23)		(20)
Group Reporting Basis Total operating income	[3]	(17)		0	(18)		(11)
Expected credit losses / provision for credit losses	[3]	(17)			330
Expected credit losses/provision for credit losses	[3]			23			64
Group Reporting Basis Revenues	[3]	0		(23)	(348)		(75)
Operating Expenses	[3]	(9)		10	85		18
Group Reporting Basis Profit (Loss) Before Income Tax	[3]	9		(33)	(433)		(93)
Total Assets	[3]	(47,514)		(31,700)	(47,514)		(31,700)
Group Reporting Basis Total loans, net	[3]	(3,931)		(2,340)	(3,931)		(2,340)
Group Reporting Basis Goodwill	[3]	100		347	100		347
Group Reporting Basis Total deposits	[3]	(4,874)		(3,434)	(4,874)		(3,434)
Group Reporting Basis Reclassifications [Member]
Operating Statistics [Line Items]
Net Interest Income	[4]	20		(73)	2		(141)
Group Reporting Basis Other operating income	[4]	(16)		74	4		143
Group Reporting Basis Total operating income	[4]	4		1	6		2
Expected credit losses / provision for credit losses	[4]	0			0
Expected credit losses/provision for credit losses	[4]			(2)			5
Group Reporting Basis Revenues	[4]	4		3	6		(3)
Operating Expenses	[4]	4		3	6		(3)
Group Reporting Basis Profit (Loss) Before Income Tax	[4]	0		0	0		0
Total Assets	[4]	0		0	0		0
Group Reporting Basis Total loans, net	[4]	5,350		3,877	5,350		3,877
Group Reporting Basis Goodwill	[4]	0		0	0		0
Group Reporting Basis Total deposits	[4]	17,377		20,314	17,377		20,314
WPB [Member] | Operating Segments [Member]
Operating Statistics [Line Items]
Net Interest Income		197		265	429		538
Group Reporting Basis Other operating income		99		104	173		194
Group Reporting Basis Total operating income		296		369	602		732
Expected credit losses / provision for credit losses		36			176
Expected credit losses/provision for credit losses				13			34
Group Reporting Basis Revenues		260		356	426		698
Operating Expenses		326		364	1,361		732
Group Reporting Basis Profit (Loss) Before Income Tax		(66)		(8)	(935)		(34)
Total Assets		61,326		50,886	61,326		50,886
Group Reporting Basis Total loans, net		24,059		23,683	24,059		23,683
Group Reporting Basis Goodwill		0		902	0		902
Group Reporting Basis Total deposits		49,871		42,942	49,871		42,942
CMB [Member] | Operating Segments [Member]
Operating Statistics [Line Items]
Net Interest Income		204		206	414		412
Group Reporting Basis Other operating income		52		60	110		121
Group Reporting Basis Total operating income		256		266	524		533
Expected credit losses / provision for credit losses		181			304
Expected credit losses/provision for credit losses				9			15
Group Reporting Basis Revenues		75		257	220		518
Operating Expenses		142		143	289		282
Group Reporting Basis Profit (Loss) Before Income Tax		(67)		114	(69)		236
Total Assets		41,511		35,568	41,511		35,568
Group Reporting Basis Total loans, net		28,125		25,792	28,125		25,792
Group Reporting Basis Goodwill		358		358	358		358
Group Reporting Basis Total deposits		39,245		24,299	39,245		24,299
GB&M [Member] | Operating Segments [Member]
Operating Statistics [Line Items]
Net Interest Income		122		156	212		329
Group Reporting Basis Other operating income		263		189	526		379
Group Reporting Basis Total operating income		385		345	738		708
Expected credit losses / provision for credit losses		19			135
Expected credit losses/provision for credit losses				3			(14)
Group Reporting Basis Revenues		366		342	603		722
Operating Expenses		201		216	393		427
Group Reporting Basis Profit (Loss) Before Income Tax		165		126	210		295
Total Assets		155,090		126,864	155,090		126,864
Group Reporting Basis Total loans, net		17,673		20,853	17,673		20,853
Group Reporting Basis Goodwill		0		0	0		0
Group Reporting Basis Total deposits		54,414		32,840	54,414		32,840
CC [Member] | Operating Segments [Member]
Operating Statistics [Line Items]
Net Interest Income		(7)		(17)	(20)		(45)
Group Reporting Basis Other operating income		85		12	61		9
Group Reporting Basis Total operating income		78		(5)	41		(36)
Expected credit losses / provision for credit losses		0			0
Expected credit losses/provision for credit losses				0			0
Group Reporting Basis Revenues		78		(5)	41		(36)
Operating Expenses		63		38	198		68
Group Reporting Basis Profit (Loss) Before Income Tax		15		(43)	(157)		(104)
Total Assets		2,449		2,445	2,449		2,445
Group Reporting Basis Total loans, net		0		0	0		0
Group Reporting Basis Goodwill		0		0	0		0
Group Reporting Basis Total deposits		$ 0		$ 0	$ 0		$ 0

[1] See Note 15, "Business Segments," for a reconciliation of total other revenues on a U.S. GAAP basis to other operating income for each business segment under the Group Reporting Basis.

[2] The following table summarizes assets and liabilities related to our consolidated variable interest entities ("VIEs") at June 30, 2020 and December 31, 2019 which are consolidated on our balance sheet. Assets and liabilities exclude intercompany balances that eliminate in consolidation. See Note 17, "Variable Interest Entities," for additional information. Assets: Loans $39 million and $0 million. Other assets $86 million and $98 million. Total assets $125 million and $98 million respectively. Liabilities: Interest, taxes and other liabilities $23 million and $38 million. Total liabilities $23 million and $38 million, respectively.

[3] Represents adjustments associated with differences between U.S. GAAP and the Group Reporting Basis.

[4] Represents differences in financial statement presentation between U.S. GAAP and the Group Reporting Basis.