v3.26.1
Borrowings - Long-term Debt Including Unamortized Debt Discounts and Premiums (Details) - USD ($)
$ in Millions
 6 Months Ended
May 21, 2036
Nov. 14, 2035
Aug. 24, 2033
May 19, 2033
Nov. 14, 2030
May 21, 2029
Nov. 17, 2028
Jul. 27, 2028
May 19, 2028
Jun. 30, 2026
Dec. 31, 2025
Debt Instrument [Line Items]                      
Finance lease liabilities                   $ 23 $ 37
Unamortized premium — net                   24 33
Debt issuance costs                   (89) (82)
Fair value hedging basis adjustments                   (231) 11
Total long-term debt                   22,669 22,199
CSC Fixed-Rate Senior Notes | 3.450% due February 13, 2026                      
Debt Instrument [Line Items]                      
Senior notes                   $ 0 350
Fixed interest rate (percent)                   3.45%  
CSC Fixed-Rate Senior Notes | 0.900% due March 11, 2026                      
Debt Instrument [Line Items]                      
Senior notes                   $ 0 1,250
Fixed interest rate (percent)                   0.90%  
CSC Fixed-Rate Senior Notes | 1.150% due May 13, 2026                      
Debt Instrument [Line Items]                      
Senior notes                   $ 0 1,000
Fixed interest rate (percent)                   1.15%  
CSC Fixed-Rate Senior Notes | 5.875% due August 24, 2026                      
Debt Instrument [Line Items]                      
Senior notes                   $ 1,000 1,000
Fixed interest rate (percent)                   5.875%  
CSC Fixed-Rate Senior Notes | 3.200% due March 2, 2027                      
Debt Instrument [Line Items]                      
Senior notes                   $ 650 650
Fixed interest rate (percent)                   3.20%  
CSC Fixed-Rate Senior Notes | 2.450% due March 3, 2027                      
Debt Instrument [Line Items]                      
Senior notes                   $ 1,500 1,500
Fixed interest rate (percent)                   2.45%  
CSC Fixed-Rate Senior Notes | 3.300% due April 1, 2027                      
Debt Instrument [Line Items]                      
Senior notes                   $ 744 744
Fixed interest rate (percent)                   3.30%  
CSC Fixed-Rate Senior Notes | 3.200% due January 25, 2028                      
Debt Instrument [Line Items]                      
Senior notes                   $ 700 700
Fixed interest rate (percent)                   3.20%  
CSC Fixed-Rate Senior Notes | 2.000% due March 20, 2028                      
Debt Instrument [Line Items]                      
Senior notes                   $ 1,250 1,250
Fixed interest rate (percent)                   2.00%  
CSC Fixed-Rate Senior Notes | 4.000% due February 1, 2029                      
Debt Instrument [Line Items]                      
Senior notes                   $ 600 600
Fixed interest rate (percent)                   4.00%  
CSC Fixed-Rate Senior Notes | 3.250% due May 22, 2029                      
Debt Instrument [Line Items]                      
Senior notes                   $ 600 600
Fixed interest rate (percent)                   3.25%  
CSC Fixed-Rate Senior Notes | 2.750% due October 1, 2029                      
Debt Instrument [Line Items]                      
Senior notes                   $ 475 475
Fixed interest rate (percent)                   2.75%  
CSC Fixed-Rate Senior Notes | 4.625% due March 22, 2030                      
Debt Instrument [Line Items]                      
Senior notes                   $ 500 500
Fixed interest rate (percent)                   4.625%  
CSC Fixed-Rate Senior Notes | 1.650% due March 11, 2031                      
Debt Instrument [Line Items]                      
Senior notes                   $ 750 750
Fixed interest rate (percent)                   1.65%  
CSC Fixed-Rate Senior Notes | 2.300% due May 13, 2031                      
Debt Instrument [Line Items]                      
Senior notes                   $ 750 750
Fixed interest rate (percent)                   2.30%  
CSC Fixed-Rate Senior Notes | 1.950% due December 1, 2031                      
Debt Instrument [Line Items]                      
Senior notes                   $ 850 850
Fixed interest rate (percent)                   1.95%  
CSC Fixed-Rate Senior Notes | 2.900% due March 3, 2032                      
Debt Instrument [Line Items]                      
Senior notes                   $ 1,000 1,000
Fixed interest rate (percent)                   2.90%  
CSC Floating-Rate Senior Notes | SOFR + 0.520% due May 13, 2026                      
Debt Instrument [Line Items]                      
Senior notes                   $ 0 500
Basis spread (percent)                   0.52%  
CSC Floating-Rate Senior Notes | SOFR + 1.050% due March 3, 2027                      
Debt Instrument [Line Items]                      
Senior notes                   $ 500 500
Basis spread (percent)                   1.05%  
CSC Fixed-To-Floating Rate Senior Notes                      
Debt Instrument [Line Items]                      
Senior notes                   $ 22,269 22,119
CSC Fixed-To-Floating Rate Senior Notes | 5.643% due May 19, 2029                      
Debt Instrument [Line Items]                      
Senior notes                   $ 1,200 1,200
Fixed interest rate (percent)                   5.643%  
CSC Fixed-To-Floating Rate Senior Notes | 5.643% due May 19, 2029 | Forecast                      
Debt Instrument [Line Items]                      
Basis spread (percent)                 2.21%    
CSC Fixed-To-Floating Rate Senior Notes | 4.603% due July 27, 2029                      
Debt Instrument [Line Items]                      
Senior notes                   $ 1,000 0
Fixed interest rate (percent)                   4.603%  
CSC Fixed-To-Floating Rate Senior Notes | 4.603% due July 27, 2029 | Forecast                      
Debt Instrument [Line Items]                      
Basis spread (percent)               0.622%      
CSC Fixed-To-Floating Rate Senior Notes | 6.196% due November 17, 2029                      
Debt Instrument [Line Items]                      
Senior notes                   $ 1,300 1,300
Fixed interest rate (percent)                   6.196%  
CSC Fixed-To-Floating Rate Senior Notes | 6.196% due November 17, 2029 | Forecast                      
Debt Instrument [Line Items]                      
Basis spread (percent)             1.878%        
CSC Fixed-To-Floating Rate Senior Notes | 4.744% due May 21, 2030                      
Debt Instrument [Line Items]                      
Senior notes                   $ 1,000 0
Fixed interest rate (percent)                   4.744%  
CSC Fixed-To-Floating Rate Senior Notes | 4.744% due May 21, 2030 | Forecast                      
Debt Instrument [Line Items]                      
Basis spread (percent)           0.78%          
CSC Fixed-To-Floating Rate Senior Notes | 4.343% due November 14, 2031                      
Debt Instrument [Line Items]                      
Senior notes                   $ 1,000 1,000
Fixed interest rate (percent)                   4.343%  
CSC Fixed-To-Floating Rate Senior Notes | 4.343% due November 14, 2031 | Forecast                      
Debt Instrument [Line Items]                      
Basis spread (percent)         0.94%            
CSC Fixed-To-Floating Rate Senior Notes | 5.853% due May 19, 2034                      
Debt Instrument [Line Items]                      
Senior notes                   $ 1,300 1,300
Fixed interest rate (percent)                   5.853%  
CSC Fixed-To-Floating Rate Senior Notes | 5.853% due May 19, 2034 | Forecast                      
Debt Instrument [Line Items]                      
Basis spread (percent)       2.50%              
CSC Fixed-To-Floating Rate Senior Notes | 6.136% due August 24, 2034                      
Debt Instrument [Line Items]                      
Senior notes                   $ 1,350 1,350
Fixed interest rate (percent)                   6.136%  
CSC Fixed-To-Floating Rate Senior Notes | 6.136% due August 24, 2034 | Forecast                      
Debt Instrument [Line Items]                      
Basis spread (percent)     2.01%                
CSC Fixed-To-Floating Rate Senior Notes | 4.914% due November 14, 2036                      
Debt Instrument [Line Items]                      
Senior notes                   $ 1,000 1,000
Fixed interest rate (percent)                   4.914%  
CSC Fixed-To-Floating Rate Senior Notes | 4.914% due November 14, 2036 | Forecast                      
Debt Instrument [Line Items]                      
Basis spread (percent)   1.23%                  
CSC Fixed-To-Floating Rate Senior Notes | 5.493% due May 21, 2037                      
Debt Instrument [Line Items]                      
Senior notes                   $ 1,250 0
Fixed interest rate (percent)                   5.493%  
CSC Fixed-To-Floating Rate Senior Notes | 5.493% due May 21, 2037 | Forecast                      
Debt Instrument [Line Items]                      
Basis spread (percent) 1.28%                    
Ameritrade Holding Senior Notes                      
Debt Instrument [Line Items]                      
Senior notes                   $ 81 81
Ameritrade Holding Fixed-Rate Senior Notes | 3.300% due April 1, 2027                      
Debt Instrument [Line Items]                      
Senior notes                   $ 56 56
Fixed interest rate (percent)                   3.30%  
Ameritrade Holding Fixed-Rate Senior Notes | 2.750% due October 1, 2029                      
Debt Instrument [Line Items]                      
Senior notes                   $ 25 25
Fixed interest rate (percent)                   2.75%  
Software License Agreement | Third-Party Long Term Software Licensing Agreement                      
Debt Instrument [Line Items]                      
Other finance liabilities                   $ 592 $ 0