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 Income / (Loss)	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
Beginning balance at Dec. 31, 2018	$ 23,847,232,000			$ 17,859,304,000	$ (321,652,000)	$ 3,783,405,000		$ 2,526,175,000
Beginning balance (ASU 2016-02) at Dec. 31, 2018		$ 18,652,000					$ 18,652,000
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Comprehensive income attributable to SHUSA	934,699,000				268,493,000	666,206,000
Other comprehensive income (loss) attributable to NCI	(19,718,000)							(19,718,000)
Net income attributable to NCI	250,086,000							250,086,000
Impact of SC stock option activity	9,555,000							9,555,000
Contribution from shareholder	88,927,000			88,927,000
Dividends declared and paid on common stock	(150,000,000)					(150,000,000)
Dividends paid to NCI	(64,493,000)							(64,493,000)
Stock repurchase attributable to NCI	(245,663,000)			5,865,000				(251,528,000)
Ending balance (in shares) at Sep. 30, 2019			530,391,000
Ending balance at Sep. 30, 2019	24,669,277,000			17,954,096,000	(53,159,000)	4,318,263,000		2,450,077,000
Beginning balance (in shares) at Dec. 31, 2018			530,391,000
Beginning balance at Dec. 31, 2018	$ 23,847,232,000			17,859,304,000	(321,652,000)	3,783,405,000		2,526,175,000
Beginning balance (ASU 2016-02) at Dec. 31, 2018		18,652,000					18,652,000
Ending balance (in shares) at Dec. 31, 2019	530,391,043		530,391,000
Ending balance at Dec. 31, 2019	$ 24,398,830,000	(1,800,000,000)		17,954,441,000	(88,207,000)	4,155,226,000		2,377,370,000
Ending balance (ASU 2016-13) at Dec. 31, 2019		(1,785,464,000)					$ (1,346,097,000)		$ (439,367,000)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Accounting Standards Update [Extensible List]	us-gaap:AccountingStandardsUpdate201613Member
Beginning balance (in shares) at Jun. 30, 2019			530,391,000
Beginning balance at Jun. 30, 2019	$ 24,504,819,000			17,945,636,000	(96,519,000)	4,114,658,000		2,541,044,000
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Comprehensive income attributable to SHUSA	246,965,000				43,360,000	203,605,000
Other comprehensive income (loss) attributable to NCI	(3,195,000)							(3,195,000)
Net income attributable to NCI	66,831,000							66,831,000
Impact of SC stock option activity	3,949,000							3,949,000
Contribution from shareholder	13,026,000			13,026,000
Dividends paid to NCI	(22,099,000)							(22,099,000)
Stock repurchase attributable to NCI	(141,019,000)			(4,566,000)				(136,453,000)
Ending balance (in shares) at Sep. 30, 2019			530,391,000
Ending balance at Sep. 30, 2019	$ 24,669,277,000			17,954,096,000	(53,159,000)	4,318,263,000		2,450,077,000
Beginning balance (in shares) at Dec. 31, 2019	530,391,043		530,391,000
Beginning balance at Dec. 31, 2019	$ 24,398,830,000	$ (1,800,000,000)		17,954,441,000	(88,207,000)	4,155,226,000		2,377,370,000
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Comprehensive income attributable to SHUSA	(940,389,000)				285,880,000	(1,226,269,000)
Other comprehensive income (loss) attributable to NCI	(8,690,000)							(8,690,000)
Net income attributable to NCI	82,087,000							82,087,000
Impact of SC stock option activity	4,642,000							4,642,000
Contribution from shareholder	0
Dividends declared and paid on common stock	(125,000,000)					(125,000,000)
Dividends paid to NCI	(50,546,000)							(50,546,000)
Stock repurchase attributable to NCI	$ (770,499,000)			(77,623,000)				(692,876,000)
Ending balance (in shares) at Sep. 30, 2020	530,391,043		530,391,000
Ending balance at Sep. 30, 2020	$ 20,804,971,000			17,876,818,000	197,673,000	1,457,860,000		1,272,620,000
Beginning balance (in shares) at Jun. 30, 2020			530,391,000
Beginning balance at Jun. 30, 2020	20,226,777,000			17,890,181,000	259,686,000	685,025,000		1,391,885,000
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Comprehensive income attributable to SHUSA	710,822,000				(62,013,000)	772,835,000
Other comprehensive income (loss) attributable to NCI	1,416,000							1,416,000
Net income attributable to NCI	101,701,000							101,701,000
Impact of SC stock option activity	1,247,000							1,247,000
Dividends paid to NCI	(13,333,000)							(13,333,000)
Stock repurchase attributable to NCI	$ (223,659,000)			(13,363,000)				(210,296,000)
Ending balance (in shares) at Sep. 30, 2020	530,391,043		530,391,000
Ending balance at Sep. 30, 2020	$ 20,804,971,000			$ 17,876,818,000	$ 197,673,000	$ 1,457,860,000		$ 1,272,620,000