Leasing Activity Leasing Activity, Lease Payments on Operating Leases Subsequent to Adoption of ASU 2016-02 - Leases (Details) $ in Millions	6 Months Ended
	Jun. 30, 2019 USD ($)
Operating Lease Liabilities, Payments Due [Abstract]
Remainder of 2019, operating leases, subsequent to adoption of ASU 2016-02	$ 566
2020, operating leases, subsequent to adoption of ASU 2016-02	1,127
2021, operating leases, subsequent to adoption of ASU 2016-02	947
2022, operating leases, subsequent to adoption of ASU 2016-02	792
2023, operating leases, subsequent to adoption of ASU 2016-02	654
Thereafter, operating leases, subsequent to adoption of ASU 2016-02	2,054
Total lease payments, operating leases, subsequent to adoption of ASU 2016-02	6,140
Less: imputed interest	838
Total operating lease liability	$ 5,302
Weighted average remaining lease term (in years)	7 years 3 months 18 days
Weighted average discount rate	3.20%
Leasing Activity Disclosures Textual [Abstract]
Operating lease, term of contract	15 years
Operating lease, term of contract, longest expiration year	2105
Operating lease, not yet commenced, lease commitment amount	$ 72
Operating lease, not yet commenced, earliest year of commencement	2020
Minimum [Member]
Leasing Activity Disclosures Textual [Abstract]
Operating lease, lease not yet commenced, term of contract	1 year
Maximum [Member]
Leasing Activity Disclosures Textual [Abstract]
Operating lease, lease not yet commenced, term of contract	11 years