CONDENSED CONSOLIDATED STATEMENTS OF STOCKHOLDER’S EQUITY - USD ($)	Total	Cumulative Effect, Period of Adoption, Adjustment	Common Shares Outstanding	Common Stock and Paid-in Capital	Accumulated Other Comprehensive (Loss)/Income	Accumulated Other Comprehensive (Loss)/Income Cumulative Effect, Period of Adoption, Adjustment	Retained Earnings	Retained Earnings Cumulative Effect, Period of Adoption, Adjustment	Noncontrolling Interest	Noncontrolling Interest Cumulative Effect, Period of Adoption, Adjustment
Beginning balance (in shares) at Dec. 31, 2018			530,391,000
Equity, beginning balance at Dec. 31, 2018	$ 23,847,232,000	$ 18,652,000		$ 17,859,304,000	$ (321,652,000)	$ 0	$ 3,783,405,000	$ 18,652,000	$ 2,526,175,000
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Comprehensive income attributable to SHUSA	687,735,000				225,133,000		462,602,000
Other comprehensive loss attributable to NCI	(16,523,000)								(16,523,000)
Net income attributable to NCI	183,255,000								183,255,000
Impact of SC stock option activity	5,606,000								5,606,000
Contribution from shareholder	75,901,000			75,901,000
Dividends declared and paid on common stock	(150,000,000)						(150,000,000)
Dividends paid to NCI	(42,394,000)								(42,394,000)
Stock repurchase attributable to NCI	(104,644,000)			10,431,000					(115,075,000)
Ending balance (in shares) at Jun. 30, 2019			530,391,000
Equity, ending balance at Jun. 30, 2019	24,504,820,000			17,945,636,000	(96,519,000)		4,114,659,000		2,541,044,000
Beginning balance (in shares) at Dec. 31, 2018			530,391,000
Equity, beginning balance at Dec. 31, 2018	$ 23,847,232,000	18,652,000		17,859,304,000	(321,652,000)	$ 0	3,783,405,000	18,652,000	2,526,175,000
Ending balance (in shares) at Dec. 31, 2019	530,391,043		530,391,000
Equity, ending balance at Dec. 31, 2019	$ 24,398,830,000	(1,785,464,000)		17,954,441,000	(88,207,000)		4,155,226,000	(1,346,097,000)	2,377,370,000	$ (439,367,000)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Accounting Standards Update [Extensible List]	us-gaap:AccountingStandardsUpdate201613Member
Beginning balance (in shares) at Mar. 31, 2019			530,391,000
Equity, beginning balance at Mar. 31, 2019	$ 24,128,405,000			17,899,170,000	(217,033,000)		3,894,037,000		2,552,231,000
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Comprehensive income attributable to SHUSA	416,136,000				120,514,000		295,622,000
Other comprehensive loss attributable to NCI	(10,180,000)								(10,180,000)
Net income attributable to NCI	110,743,000								110,743,000
Impact of SC stock option activity	1,255,000								1,255,000
Contribution from shareholder	41,570,000			41,570,000
Dividends declared and paid on common stock	(75,000,000)						(75,000,000)
Dividends paid to NCI	(21,245,000)								(21,245,000)
Stock repurchase attributable to NCI	(86,864,000)			4,896,000					(91,760,000)
Ending balance (in shares) at Jun. 30, 2019			530,391,000
Equity, ending balance at Jun. 30, 2019	$ 24,504,820,000			17,945,636,000	(96,519,000)		4,114,659,000		2,541,044,000
Beginning balance (in shares) at Dec. 31, 2019	530,391,043		530,391,000
Equity, beginning balance at Dec. 31, 2019	$ 24,398,830,000	(1,785,464,000)		17,954,441,000	(88,207,000)		4,155,226,000	(1,346,097,000)	2,377,370,000	(439,367,000)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Comprehensive income attributable to SHUSA	(1,651,211,000)				347,893,000		(1,999,104,000)
Other comprehensive loss attributable to NCI	(10,106,000)								(10,106,000)
Net income attributable to NCI	(19,614,000)								(19,614,000)
Impact of SC stock option activity	3,394,000								3,394,000
Contribution from shareholder	0
Dividends declared and paid on common stock	(125,000,000)						(125,000,000)
Dividends paid to NCI	(37,212,000)								(37,212,000)
Stock repurchase attributable to NCI	$ (546,840,000)			(64,260,000)					(482,580,000)
Ending balance (in shares) at Jun. 30, 2020	530,391,043		530,391,000
Equity, ending balance at Jun. 30, 2020	$ 20,226,777,000			17,890,181,000	259,686,000		685,025,000		1,391,885,000
Beginning balance (in shares) at Mar. 31, 2020			530,391,000
Equity, beginning balance at Mar. 31, 2020	22,223,973,000	$ (132,000)		17,870,442,000	266,981,000		2,557,302,000	$ 150,000	1,529,248,000	$ (282,000)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Comprehensive income attributable to SHUSA	(1,879,722,000)				(7,295,000)		(1,872,427,000)
Other comprehensive loss attributable to NCI	27,000								27,000
Net income attributable to NCI	(23,377,000)								(23,377,000)
Impact of SC stock option activity	1,001,000								1,001,000
Dividends paid to NCI	(16,619,000)								(16,619,000)
Stock repurchase attributable to NCI	$ (78,374,000)			19,739,000					(98,113,000)
Ending balance (in shares) at Jun. 30, 2020	530,391,043		530,391,000
Equity, ending balance at Jun. 30, 2020	$ 20,226,777,000			$ 17,890,181,000	$ 259,686,000		$ 685,025,000		$ 1,391,885,000