Guarantees and Contingent Liabilities (Details)		6 Months Ended	28 Months Ended
	Jan. 30, 2018 judgment plaintiff	Jun. 30, 2018 USD ($) appeal	Dec. 31, 2003 case	May 08, 2018 USD ($)
Proceedings:
Number of appeals | appeal		3
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		$ 145,000,000
Judicial Ruling
Proceedings:
Loss contingency, number of plaintiffs | plaintiff	27
Texas Windstorm Insurance Association
Proceedings:
Loss contingency, loss accrual				$ 37,000,000