Lease Commitments - Assets and Liabilities of Lessee (Details) $ in Millions	Mar. 31, 2019 USD ($)
Assets
Operating lease right-of-use assets	$ 993
Finance lease assets	70
Total lease assets	1,063
Current lease liabilities
Operating	214
Finance	27
Non-current lease liabilities
Operating	978
Finance	50
Total lease liabilities	$ 1,269