Summary of Significant Accounting Policies Equity investment and excess costs (Details) - USD ($) $ in Millions |
12 Months Ended | |
---|---|---|
Dec. 31, 2018 |
Dec. 31, 2017 |
|
Schedule of Equity Method Investments [Line Items] | ||
Equity Method Investment, Difference Between Carrying Amount and Underlying Equity, Amortization Period | 12 years | |
Amortized [Member] | ||
Schedule of Equity Method Investments [Line Items] | ||
Equity Method of Accounting and Excess Investment Cost | $ 470 | $ 732 |
Not Subject To Amortization But Subject to Impairment [Member] | ||
Schedule of Equity Method Investments [Line Items] | ||
Equity Method of Accounting and Excess Investment Cost | $ 1,967 | $ 1,967 |