Fair Value (Summary of Net Gains and Losses Recognized for Investments In Equity Securities between Investments Sold and Investments Held) (Details) $ in Millions	12 Months Ended
Dec. 31, 2018 USD ($)
Equity Securities, FV-NI, Realized Gain (Loss)	$ (7)
Available-for-sale Securities [Member]
Equity Securities, FV-NI, Realized Gain (Loss)	1
Held-to-maturity Securities [Member]
Equity Securities, FV-NI, Unrealized Gain (Loss)	$ (8)

Amount of realized gain (loss) from sale of investment in equity security measured at fair value with change in fair value recognized in net income (FV-NI).

Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 321
-SubTopic 10
-Section 50
-Paragraph 4
-URI http://asc.fasb.org/extlink&oid=84241550&loc=SL75117546-209714

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Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration