Capital Transactions - Dividends (Details) - USD ($) $ / shares in Units, $ in Millions					3 Months Ended	9 Months Ended
May 09, 2019	Feb. 12, 2019	May 09, 2018	Feb. 08, 2018	Mar. 31, 2019	Mar. 31, 2018	Sep. 30, 2019	Sep. 30, 2018
Dividends
Dividends per common share (in dollars per share)		$ 0.37		$ 0.34	$ 0.37	$ 0.34
Cash dividend payment	$ 283		$ 259				$ 283	$ 259

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