Commitments, Contingencies and Other Regulatory Matters (Details) $ / shares in Units, $ in Millions			3 Months Ended	12 Months Ended
	Oct. 20, 2014	May. 16, 2011	Mar. 31, 2016 USD ($) $ / principal_amount	Dec. 31, 2003 USD ($)	Apr. 30, 2013 $ / shares
Loss Contingencies [Line Items]
Commitments to fund partnerships			$ 52
Time deposit maturities, next rolling twelve months			$ 26
Supply Commitment [Line Items]
Trust preferred securities contractual time period			30 years
Liquidation amount per trust preferred security | $ / principal_amount			1,000
Estimated maximum potential liability trust preferred securities			$ 418
Unfunded Commitments to Extend Credit [Member]
Supply Commitment [Line Items]
Unfunded Commitments To Extend Credit			$ 55
Axajo Complaint [Member]
Loss Contingencies [Line Items]
Loss Contingency, Damages Awarded, Value				$ 1
Droplets Inc Complaint [Member]
Loss Contingencies [Line Items]
Loss Contingency, Patents Allegedly Infringed, Number		2
John Scranton Complaint [Member]
Loss Contingencies [Line Items]
Alleged Minimum Amount Company Would Exercise Options At Expiration | $ / shares					$ 0.01
John Scranton Complaint [Member] | Judicial Ruling With Prejudice [Member]
Loss Contingencies [Line Items]
Loss Contingency, Claims Dismissed, Number	4
John Scranton Complaint [Member] | Judicial Ruling Without Prejudice [Member]
Loss Contingencies [Line Items]
Loss Contingency, Claims Dismissed, Number	2