Allowance for Loan and Lease Losses Allowance for Loan and Lease Losses - Loss Sharing Arrangements (Details) - Loss Sharing Agreement [Member] - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Financing Receivable, Allowance for Credit Losses [Roll Forward]
Expected reimbursement from loss sharing partners	$ 380	$ 228	$ 194	$ 143
Amounts charged to partners and impacting net charge-offs	(285)	(229)	(189)
Impact to provision for credit losses	$ 437	$ 263	$ 240