Business Segments - Summary on Reconciliation of Results Under Ifrs to Us Gaap (Detail) - USD ($) $ in Millions		3 Months Ended			9 Months Ended
		Sep. 30, 2020		Sep. 30, 2019	Sep. 30, 2020		Sep. 30, 2019	Dec. 31, 2019
Operating Statistics [Line Items]
Net Interest Income		$ 485		$ 543	$ 1,520		$ 1,777
Group Reporting Basis Other operating income		433		438	1,303		1,141
Group Reporting Basis Total operating income		918		981	2,823		2,918
Expected credit losses / provision for credit losses		(15)			600
Expected credit losses/provision for credit losses				68			103
Group Reporting Basis Revenues		933		913	2,223		2,815
Operating Expenses		1,054		946	3,295		2,455
Group Reporting Basis Profit (Loss) Before Income Tax		(121)		(33)	(1,072)		360
Total Assets		232,867		222,515	232,867		222,515
Group Reporting Basis Total loans, net		63,795		69,175	63,795		69,175
Group Reporting Basis Goodwill		358		1,051	358		1,051
Group Reporting Basis Total deposits		139,779		103,964	139,779		103,964
Net interest income		548		503	1,590		1,605
Other operating income	[1]	356		486	1,207		1,312
Total operating income		904		989	2,797		2,917
Provision for credit losses		(105)			840
Provision for credit losses		(75)		94	774		198
Total income		1,009		895	1,957		2,719
Operating expenses		785		1,106	3,117		2,630
Income (loss) before income tax		224		(211)	(1,160)		89
Total assets		200,946	[2]	184,760	200,946	[2]	184,760	$ 175,375	[2]
Total loans, net		65,325		70,660	65,325		70,660	67,916
Goodwill		458		1,242	458		1,242	1,242
Total deposits		150,328		119,801	150,328		119,801	$ 119,693
Group Reporting Basis Adjustments [Member]
Operating Statistics [Line Items]
Net Interest Income	[3]	1		1	6		10
Group Reporting Basis Other operating income	[3]	(22)		2	(45)		(18)
Group Reporting Basis Total operating income	[3]	(21)		3	(39)		(8)
Expected credit losses / provision for credit losses	[3]	(90)			240
Expected credit losses/provision for credit losses	[3]			25			89
Group Reporting Basis Revenues	[3]	69		(22)	(279)		(97)
Operating Expenses	[3]	(276)		156	(191)		174
Group Reporting Basis Profit (Loss) Before Income Tax	[3]	345		(178)	(88)		(271)
Total Assets	[3]	(31,921)		(37,755)	(31,921)		(37,755)
Group Reporting Basis Total loans, net	[3]	(1,682)		(1,965)	(1,682)		(1,965)
Group Reporting Basis Goodwill	[3]	100		191	100		191
Group Reporting Basis Total deposits	[3]	(5,198)		(4,036)	(5,198)		(4,036)
Group Reporting Basis Reclassifications [Member]
Operating Statistics [Line Items]
Net Interest Income	[4]	62		(41)	64		(182)
Group Reporting Basis Other operating income	[4]	(55)		46	(51)		189
Group Reporting Basis Total operating income	[4]	7		5	13		7
Expected credit losses / provision for credit losses	[4]	0			0
Expected credit losses/provision for credit losses	[4]			1			6
Group Reporting Basis Revenues	[4]	7		4	13		1
Operating Expenses	[4]	7		4	13		1
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]	3,212		3,450	3,212		3,450
Group Reporting Basis Goodwill	[4]	0		0	0		0
Group Reporting Basis Total deposits	[4]	15,747		19,873	15,747		19,873
WPB [Member] | Operating Segments [Member]
Operating Statistics [Line Items]
Net Interest Income		200		253	629		791
Group Reporting Basis Other operating income		110		99	283		293
Group Reporting Basis Total operating income		310		352	912		1,084
Expected credit losses / provision for credit losses		12			188
Expected credit losses/provision for credit losses				52			86
Group Reporting Basis Revenues		298		300	724		998
Operating Expenses		527		557	1,888		1,289
Group Reporting Basis Profit (Loss) Before Income Tax		(229)		(257)	(1,164)		(291)
Total Assets		56,728		52,334	56,728		52,334
Group Reporting Basis Total loans, net		23,821		23,908	23,821		23,908
Group Reporting Basis Goodwill		0		693	0		693
Group Reporting Basis Total deposits		48,477		43,974	48,477		43,974
CMB [Member] | Operating Segments [Member]
Operating Statistics [Line Items]
Net Interest Income		202		216	616		628
Group Reporting Basis Other operating income		66		66	176		187
Group Reporting Basis Total operating income		268		282	792		815
Expected credit losses / provision for credit losses		(21)			283
Expected credit losses/provision for credit losses				19			34
Group Reporting Basis Revenues		289		263	509		781
Operating Expenses		150		145	439		427
Group Reporting Basis Profit (Loss) Before Income Tax		139		118	70		354
Total Assets		38,096		36,968	38,096		36,968
Group Reporting Basis Total loans, net		25,852		26,459	25,852		26,459
Group Reporting Basis Goodwill		358		358	358		358
Group Reporting Basis Total deposits		39,736		25,975	39,736		25,975
GB&M [Member] | Operating Segments [Member]
Operating Statistics [Line Items]
Net Interest Income		92		85	304		414
Group Reporting Basis Other operating income		217		269	743		648
Group Reporting Basis Total operating income		309		354	1,047		1,062
Expected credit losses / provision for credit losses		(6)			129
Expected credit losses/provision for credit losses				(3)			(17)
Group Reporting Basis Revenues		315		357	918		1,079
Operating Expenses		251		200	644		627
Group Reporting Basis Profit (Loss) Before Income Tax		64		157	274		452
Total Assets		136,478		130,708	136,478		130,708
Group Reporting Basis Total loans, net		14,122		18,808	14,122		18,808
Group Reporting Basis Goodwill		0		0	0		0
Group Reporting Basis Total deposits		51,566		34,015	51,566		34,015
CC [Member] | Operating Segments [Member]
Operating Statistics [Line Items]
Net Interest Income		(9)		(11)	(29)		(56)
Group Reporting Basis Other operating income		40		4	101		13
Group Reporting Basis Total operating income		31		(7)	72		(43)
Expected credit losses / provision for credit losses		0			0
Expected credit losses/provision for credit losses				0			0
Group Reporting Basis Revenues		31		(7)	72		(43)
Operating Expenses		126		44	324		112
Group Reporting Basis Profit (Loss) Before Income Tax		(95)		(51)	(252)		(155)
Total Assets		1,565		2,505	1,565		2,505
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] Assets

[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.