Parent Company Financial Information (Parent Company Only) (Schedule Of Balance Sheets) (Details) (USD $) In Thousands, except Share data, unless otherwise specified	Sep. 30, 2014	Sep. 30, 2013	Sep. 30, 2012	Sep. 30, 2011
ASSETS:
Cash and cash equivalents	$ 810,840	$ 113,886	$ 141,705	$ 121,070
Other assets	143,945	127,063
TOTAL ASSETS	9,865,028	9,186,449
LIABILITIES:
Accounts payable and accrued expenses	46,357	31,402
STOCKHOLDERS' EQUITY:
Preferred stock ($0.01 par value) 100,000,000 shares authorized; no shares issued or outstanding	0	0
Common stock ($0.01 par value) 1,400,000,000 shares authorized; 140,951,203 and 147,840,268 shares issued and outstanding as of September 30, 2014 and 2013, respectively	1,410	1,478
Additional paid-in capital	1,180,732	1,235,781
Unearned compensation - ESOP	(42,951)	(44,603)
Retained earnings	346,705	432,203
AOCI, net of tax	6,986	7,267
Total stockholders' equity	1,492,882	1,632,126	1,806,458	1,939,529
TOTAL LIABILITIES AND STOCKHOLDERS' EQUITY	9,865,028	9,186,449
Preferred stock, par value	$ 0.01	$ 0.01
Preferred stock, shares authorized	100,000,000	100,000,000
Preferred stock, shares issued	0	0
Preferred stock, shares outstanding	0	0
Common stock, par value	$ 0.01	$ 0.01
Common stock, shares authorized	1,400,000,000	1,400,000,000
Common stock, shares issued	140,951,203	147,840,268
Common stock, shares outstanding	140,951,203	147,840,268
Capitol Federal Financial Inc [Member]
ASSETS:
Cash and cash equivalents	139,540	207,012	308,648	113,101
Investment in the Bank	1,306,351	1,370,426
Note receivable - ESOP	46,140	47,260
Other assets	484	282
Income tax receivable	3,618	3,031
Deferred income tax assets	393	4,186
TOTAL ASSETS	1,496,526	1,632,197
LIABILITIES:
Accounts payable and accrued expenses	3,644	71
STOCKHOLDERS' EQUITY:
Preferred stock ($0.01 par value) 100,000,000 shares authorized; no shares issued or outstanding	0	0
Common stock ($0.01 par value) 1,400,000,000 shares authorized; 140,951,203 and 147,840,268 shares issued and outstanding as of September 30, 2014 and 2013, respectively	1,410	1,478
Additional paid-in capital	1,180,732	1,235,781
Unearned compensation - ESOP	(42,951)	(44,603)
Retained earnings	346,705	432,203
AOCI, net of tax	6,986	7,267
Total stockholders' equity	1,492,882	1,632,126
TOTAL LIABILITIES AND STOCKHOLDERS' EQUITY	$ 1,496,526	$ 1,632,197
Preferred stock, par value	$ 0.01	$ 0.01
Preferred stock, shares authorized	100,000,000	100,000,000
Preferred stock, shares issued	0	0
Preferred stock, shares outstanding	0	0
Common stock, par value	$ 0.01	$ 0.01
Common stock, shares authorized	1,400,000,000	1,400,000,000
Common stock, shares issued	140,951,203	147,840,268
Common stock, shares outstanding	140,951,203	147,840,268