Borrowings (Credit Facilities Narrative) (Details) - USD ($)	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015
Line of Credit Facility [Line Items]
Purchase of FHLB stock	$ 152,000,000
FHLB stock sold	88,000,000	$ 8,000,000
CSC’s stockholders’ equity, excluding accumulated other comprehensive income	16,600,000,000
Commercial paper [Member]
Line of Credit Facility [Line Items]
Line of credit facility, maximum borrowing capacity	1,500,000,000
Commercial Paper Notes, amount outstanding	0	0
Revolving Credit Facility [Member]
Line of Credit Facility [Line Items]
Line of credit facility, maximum borrowing capacity	750,000,000
Standby letters of credit [Member]
Line of Credit Facility [Line Items]
Line of credit facility, current borrowing capacity	295,000,000
Schwab Bank [Member]
Line of Credit Facility [Line Items]
Purchase of FHLB stock	152,000,000
FHLB stock sold	88,000,000	8,000,000
Schwab Bank [Member] | Secured Credit Facility [Member]
Line of Credit Facility [Line Items]
Borrowings on line of credit	0	0
Group of banks facility [Member] | Line of credit [Member]
Line of Credit Facility [Line Items]
Borrowings on line of credit	0	0
Line of credit facility, maximum borrowing capacity	$ 750,000,000
Unsecured credit facility, expiration date	Jun. 01, 2017
Minimum level of stockholders' equity required under credit facility	$ 10,200,000,000
Group of banks [Member] | Line of credit [Member]
Line of Credit Facility [Line Items]
Borrowings on line of credit	$ 0	$ 0
Maximum [Member] | Commercial paper [Member]
Line of Credit Facility [Line Items]
Debt instrument term	270 days