Debt (Corporate Revolving Facility and other Letters of Credit Facilities) (Details) - USD ($) $ in Millions	3 Months Ended		12 Months Ended
	Sep. 30, 2019	Jun. 30, 2019	Dec. 31, 2019	Aug. 12, 2019	Apr. 05, 2019	Dec. 31, 2018
Line of Credit Facility [Line Items]
Debt and Lease Obligation			$ 11,706			$ 10,785
Letters of Credit Outstanding, Amount			1,085			1,365
CDHI [Member]
Line of Credit Facility [Line Items]
Debt and Lease Obligation			$ 122
Applicable margin range percentage above base rate			1.75%
Applicable Margin Range Percentage Above British Bankers' Association Interest Settlement Rates			2.75%
Revolving Credit Facility [Member]
Line of Credit Facility [Line Items]
Letters of Credit Outstanding, Amount			$ 604			693
Revolving Credit Facility [Member] | Amendment No. 9 [Member]
Line of Credit Facility [Line Items]
Line of Credit Facility, Increase (Decrease), Net		$ 330
Line of Credit Facility, Maximum Borrowing Capacity					$ 2,020
Revolving Credit Facility [Member] | Amendment No. 8 [Member]
Line of Credit Facility [Line Items]
Line of Credit Facility, Maximum Borrowing Capacity		$ 1,690
Revolving Credit Facility [Member] | Amendment No. 10 [Member]
Line of Credit Facility [Line Items]
Line of Credit Facility, Increase (Decrease), Net	$ 20
Line of Credit Facility, Maximum Borrowing Capacity				$ 2,000
Total Letter of Credit Sub-limit				$ 150
Standby Letters of Credit [Member]
Line of Credit Facility [Line Items]
Letters of Credit Outstanding, Amount			3			251
Various Project Financing Facilities [Member]
Line of Credit Facility [Line Items]
Letters of Credit Outstanding, Amount			184			228
Other Corporate Facilities [Member]
Line of Credit Facility [Line Items]
Letters of Credit Outstanding, Amount			294			193
Line of Credit Facility, Maximum Borrowing Capacity			300
Other Corporate Facilities [Member] | Goldman Sachs Facility 2 [Member]
Line of Credit Facility [Line Items]
Line of Credit Facility, Maximum Borrowing Capacity			100
Revolving Credit Facility [Member]
Line of Credit Facility [Line Items]
Debt and Lease Obligation			$ 122			$ 30