Financing Activities - Distributions (Details) - $ / shares		3 Months Ended
Feb. 28, 2019	Mar. 31, 2019	Mar. 31, 2018
Distributions (Numeric) [Abstract]
Current quarterly common stock dividend (in dollars per share)	$ 0.4125	$ 0.4125	$ 0.4100
Annualized current quarterly common stock dividend (in dollars per share)	$ 1.65

Aggregate dividends declared during the period for each share of common stock outstanding.

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 505
-SubTopic 10
-Section S99
-Paragraph 1
-Subparagraph (SX 210.3-04)
-URI http://asc.fasb.org/extlink&oid=27012166&loc=d3e187085-122770

Name:	us-gaap_CommonStockDividendsPerShareDeclared
Namespace Prefix:	us-gaap_
Data Type:	num:perShareItemType
Balance Type:	na
Period Type:	duration