Commitments, Contingencies and Other Regulatory Matters (Details) $ / shares in Units, $ in Millions		12 Months Ended
	May 16, 2011	Dec. 31, 2017 USD ($) $ / CapitalSecurity	Dec. 31, 2003 USD ($)	Apr. 30, 2013 $ / shares
Loss Contingencies [Line Items]
Commitments to fund partnerships		$ 99
Time deposit maturities, next rolling twelve months		$ 21
Trust preferred securities contractual time period		30 years
Liquidation amount per trust preferred security | $ / CapitalSecurity		1,000
Estimated maximum potential liability trust preferred securities		$ 416
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