Share-Based Compensation (Threadneedle Equity Incentive Plan) (Details 5) - USD ($) $ in Millions	12 Months Ended
Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Equity Incentive Plan and Equity Participation Plan [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Employee service share-based compensation, cash flow effect, cash used to settle awards	$ 0	$ 2	$ 28

Aggregate cash paid by the entity during the period to settle equity instruments granted under equity-based payment arrangements.

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 718
-SubTopic 10
-Section 50
-Paragraph 2
-Subparagraph (k)
-URI http://asc.fasb.org/extlink&oid=96867065&loc=d3e5070-113901

Name:	us-gaap_EmployeeServiceShareBasedCompensationCashFlowEffectCashUsedToSettleAwards
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration