Significant Accounting Policies Significant Accounting Policies Additional Information (Details) - USD ($) $ in Millions	3 Months Ended	9 Months Ended
	Sep. 30, 2019	Sep. 30, 2019	Jan. 01, 2019
Significant Accounting Policies [Line Items]
Operating and Finance Lease Liabilities	$ 1,215	$ 1,215
Operating and Finance Lease, Right-of-Use Asset	1,134	1,134
Interest Received from Sales-Type and Direct Financing Leases	$ 36	$ 106
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