Significant Accounting Policies Significant Accounting Policies Additional Information (Details) - USD ($) $ in Millions	3 Months Ended	6 Months Ended
	Jun. 30, 2019	Jun. 30, 2019	Jan. 01, 2019
Significant Accounting Policies [Line Items]
Operating and Finance Lease Liabilities	$ 1,232	$ 1,232
Operating and Finance Lease, Right-of-Use Asset	1,153	1,153
Interest Received from Sales-Type and Direct Financing Leases	$ 36	$ 70
Adoption of ASU 2016-02 [Member]
Significant Accounting Policies [Line Items]
Sale Leaseback Transaction, Deferred Gain, Gross			$ 31
Operating and Finance Lease Liabilities			1,300
Operating and Finance Lease, Right-of-Use Asset			$ 1,200