Investments (Other Investments) (Details) $ in Millions |
12 Months Ended | |
|---|---|---|
|
Dec. 31, 2018
USD ($)
preferred_stock_series
|
Dec. 31, 2017
USD ($)
|
|
| Air Touch [Member] | ||
| Schedule of Other Investments [Line Items] | ||
| Number of series of preferred stock | preferred_stock_series | 3 | |
| Preferred stock aggregate redemption value | $ 1,750 | |
| Redeemable subsidiary preferred shares | 1,600 | $ 1,600 |
| Nonredeemable subsidiary preferred shares | 100 | 100 |
| Level 2 [Member] | Air Touch [Member] | ||
| Schedule of Other Investments [Line Items] | ||
| Fair value of redeemable preferred shares | $ 1,700 | 1,700 |
| Air Touch [Member] | ||
| Schedule of Other Investments [Line Items] | ||
| Number of series of preferred stock | preferred_stock_series | 2 | |
| Held to maturity investment | $ 1,600 | 1,600 |
| Preferred stock aggregate redemption value | 1,650 | |
| Air Touch [Member] | Level 2 [Member] | ||
| Schedule of Other Investments [Line Items] | ||
| Fair value of held to maturity investment redeemable preferred shares | $ 1,700 | $ 1,700 |