Bonds or similar securities issued by state, city, or local governments or the agencies operated by state, city, or local governments which are short-term, highly liquid investments that are both readily convertible to known amounts of cash and so near their maturity that they present insignificant risk of changes in value because of changes in interest rates. Generally, only investments with original maturities of three months or less qualify under that definition. Original maturity means original maturity to the entity holding the investment. For example, both a three-month US Treasury bill and a three-year Treasury note purchased three months from maturity qualify as cash equivalents. However, a Treasury note purchased three-years ago does not become a cash equivalent when its remaining maturity is three months.

No definition available.

Name:	us-gaap_MunicipalDebtSecuritiesAtCarryingValue
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

Supplemental Cash Flow Information - Narrative (Details) - USD ($) $ / shares in Units, $ in Millions	1 Months Ended
	Dec. 31, 2014	Dec. 31, 2017	Dec. 31, 2016
Transactions related to investing activities with significant non-cash components
Dividends that have been declared but paid in subsequent period (in dollars per share)	$ 1.025
City of Nevada, MO
Transactions related to investing activities with significant non-cash components
City of Nevada, MO Municipal Bond Value		$ 13	$ 12