Investments Schedule of Gains and Losses on Equity and Other Investments (Details) - USD ($) $ in Millions	3 Months Ended	6 Months Ended
Jun. 30, 2019	Jun. 30, 2018	Jun. 30, 2019	Jun. 30, 2018
Equity Securities [Member]
Gain (Loss) on Securities [Line Items]
Equity Securities, FV-NI, Realized Gain (Loss)	$ 5	$ (2)	$ 63	$ (13)
Other Investments [Member]
Gain (Loss) on Securities [Line Items]
Net gains (losses) recognized during the period	30	(11)	(14)	18
Accounting Standards Update 2016-01 [Member] \| Equity Securities [Member]
Gain (Loss) on Securities [Line Items]
Equity Securities, FV-NI, Realized Gain (Loss)	5	(2)	63	(13)
Less: Net gains (losses) recognized from sales of securities	32	5	33	15
Unrealized gains (losses) recognized for securities still held at reporting date	(27)	(7)	30	(28)
Accounting Standards Update 2016-01 [Member] \| Other Investments [Member]
Gain (Loss) on Securities [Line Items]
Net gains (losses) recognized during the period	30	(11)	(14)	18
Less: Net gains (losses) recognized from sales of securities	0	0	(2)	0
Unrealized gains (losses) recognized for securities still held at reporting date	30	(11)	(12)	18
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	35	(13)	49	5
Less: Net gains (losses) recognized from sales of securities	32	5	31	15
Unrealized gains (losses) recognized for securities still held at reporting date	$ 3	$ (18)	$ 18	$ (10)

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.

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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
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The net change in the difference between the fair value and the carrying value, or in the comparative fair values, of investments, not including unrealized gains or losses on securities separately or otherwise categorized as trading, available-for-sale, or held-to-maturity, held at each balance sheet date and included in earnings for the period.

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