Investments Schedule of Gains and Losses on Equity and Other Investments (Details) - USD ($) $ in Millions	3 Months Ended
Mar. 31, 2019	Mar. 31, 2018
Equity Securities [Member]
Gain (Loss) on Securities [Line Items]
Equity Securities, FV-NI, Realized Gain (Loss)	$ 58	$ (11)
Other Investments [Member]
Gain (Loss) on Securities [Line Items]
Net gains (losses) recognized during the period	(44)	29
Accounting Standards Update 2016-01 [Member] \| Equity Securities [Member]
Gain (Loss) on Securities [Line Items]
Equity Securities, FV-NI, Realized Gain (Loss)	58	(11)
Less: Net gains (losses) recognized from sales of securities	1	10
Unrealized gains (losses) recognized for securities still held at reporting date	57	(21)
Accounting Standards Update 2016-01 [Member] \| Other Investments [Member]
Gain (Loss) on Securities [Line Items]
Net gains (losses) recognized during the period	(44)	29
Less: Net gains (losses) recognized from sales of securities	(2)	0
Unrealized gains (losses) recognized for securities still held at reporting date	(42)	29
Accounting Standards Update 2016-01 [Member] \| Equity securities and other investments [Member]
Gain (Loss) on Securities [Line Items]
Net gains (losses) recognized during the period	14	18
Less: Net gains (losses) recognized from sales of securities	(1)	10
Unrealized gains (losses) recognized for securities still held at reporting date	$ 15	$ 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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The net realized gain (loss) on investments sold during the period, not including gains (losses) on securities separately or otherwise categorized as trading, available-for-sale, or held-to-maturity, which, for cash flow reporting, is a component of proceeds from investing activities.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 230
-SubTopic 10
-Section 45
-Paragraph 28
-Subparagraph (b)
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The net realized gains or losses on investments during the period, not including gains or losses on securities separately or otherwise categorized as trading, available-for-sale, or held-to-maturity.

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Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 944
-SubTopic 220
-Section S99
-Paragraph 1
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