Guarantees and Contingent Liabilities (Details)			1 Months Ended	3 Months Ended	28 Months Ended
	Apr. 11, 2018 plaintiff	Jan. 30, 2018 judgment plaintiff	Mar. 31, 2018 plaintiff	Mar. 31, 2018 USD ($)	Dec. 31, 2003 case
Proceedings:
Number of class action cases | case					3
Loss contingency, number of summary judgments | judgment		2
Minimum
Proceedings:
Loss contingencies, reasonably possible pretax loss exposure in excess of the amount accrued | $				$ 0
Maximum
Proceedings:
Loss contingencies, reasonably possible pretax loss exposure in excess of the amount accrued | $				$ 150,000,000
Judicial Ruling
Proceedings:
Loss contingency, number of plaintiffs		27
Settled Litigation
Proceedings:
Loss contingency, number of plaintiffs			457
Pending Litigation
Proceedings:
Loss contingency, number of plaintiffs			36
Subsequent Event | Pending Litigation
Proceedings:
Loss contingency, number of plaintiffs	14