Shareholders' Equity - Summary of Preferred Stock (Details) - USD ($) $ in Millions	Sep. 30, 2018	Dec. 31, 2017
Class of Stock [Line Items]
Carrying Amount	$ 3,053	$ 3,053

Aggregate par value plus amounts in excess of par or issuance value (in cases of no-par value stock) for nonredeemable preferred stock (or preferred stock redeemable solely at the option of the issuer) issued and outstanding, net of discount on shares. Aggregate for preferred stock issued and outstanding.

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 210
-SubTopic 10
-Section S99
-Paragraph 1
-Subparagraph (SX 210.5-02(28))
-URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682

Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 505
-SubTopic 10
-Section S99
-Paragraph 2
-Subparagraph (SX 210.4-07)
-URI http://asc.fasb.org/extlink&oid=27012166&loc=d3e187103-122770

Reference 3: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 210
-SubTopic 10
-Section S99
-Paragraph 1
-Subparagraph (SX 210.5-02(30)(a)(1))
-URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682

Name:	us-gaap_PreferredStockIncludingAdditionalPaidInCapitalNetOfDiscount
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant