Commitments, Guarantees and Contingent Liabilities - Other Narrative (Details) $ in Millions						1 Months Ended			12 Months Ended
	Jan. 30, 2018 plaintiff judgment	Dec. 31, 2017 plaintiff	Jul. 06, 2016 plaintiff	May 20, 2016 plaintiff	Jan. 01, 2015 plaintiff	Jun. 30, 2017 plaintiff trial	Dec. 31, 2016 plaintiff	Jun. 30, 2015 plaintiff	Dec. 31, 2017 USD ($)	Dec. 31, 2001 employee case	Apr. 08, 2016 adjuster
Loss Contingencies
Loss contingency, new claims filed | case										2
Loss contingency, number of plaintiffs (in plaintiffs, in cases)			118	498	460		118	10		32
Loss contingency, number of trials | trial						2
Minimum
Loss Contingencies
Loss contingencies, reasonably possible pretax loss exposure in excess of the amount accrued | $									$ 0
Maximum
Loss Contingencies
Loss contingencies, reasonably possible pretax loss exposure in excess of the amount accrued | $									$ 240
Pending Litigation
Loss Contingencies
Loss contingency, number of plaintiffs (in plaintiffs, in cases)		410				8
Judicial Ruling
Loss Contingencies
Loss contingency, number of plaintiffs (in plaintiffs, in cases)						1
Fair Labor Standards Act
Loss Contingencies
Number of cases pending (in adjusters, in claims) | adjuster											105
New York Labor Law
Loss Contingencies
Number of cases pending (in adjusters, in claims) | adjuster											137
Signed Releases Knowingly and Voluntarily
Loss Contingencies
Loss contingency, number of plaintiffs (in plaintiffs, in cases)								2
Did Not Sign Releases Knowingly and Voluntarily
Loss Contingencies
Loss contingency, number of plaintiffs (in plaintiffs, in cases)								8
Plaintiffs Asserted Suffered Loss
Loss Contingencies
Loss contingency, number of plaintiffs (in plaintiffs, in cases)							2
Phase III | Pending Litigation
Loss Contingencies
Loss contingency, number of plaintiffs (in plaintiffs, in cases)		8
Individual Plaintiffs | Settled Litigation
Loss Contingencies
Loss contingency, number of plaintiffs (in plaintiffs, in cases)		4
Individual Plaintiffs | Pending Litigation
Loss Contingencies
Loss contingency, number of plaintiffs (in plaintiffs, in cases)		85
Subsequent Event
Loss Contingencies
Loss contingency, number of summary judgments | judgment	2
Subsequent Event | Judicial Ruling
Loss Contingencies
Loss contingency, number of plaintiffs (in plaintiffs, in cases)	27