Contingent Liabilities (Narrative) (Details) - USD ($) shares in Millions	3 Months Ended	12 Months Ended
	Sep. 30, 2015	Dec. 31, 2013	Dec. 31, 2014
Commitments and Contingencies Disclosure [Line Items]
Commitments and letters of credit	$ 36,500,000,000		$ 35,100,000,000
Standby letters of credit outstanding	$ 4,300,000,000		4,500,000,000
Minimum securities lending related collateral percentage	100.00%
Possible loss in future periods in excess of accrual	$ 125,000,000
Legal settlement charge		$ 19,200,000
Remaining Visa shares held by Northern Trust, original cost basis	0
Visa Class B
Commitments and Contingencies Disclosure [Line Items]
Net pre-tax gain on redemption of Visa common stock	$ 99,900,000
Number of common stock shares sold	1.0
Remaining Visa shares held by Northern Trust	5.2
Indemnification Agreement
Commitments and Contingencies Disclosure [Line Items]
Collateralized securities loaned, subject to indemnification	$ 110,100,000,000		98,100,000,000
Credit loss liability	$ 0		$ 0