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