Leases (Maturities of Operating Lease Liabilities) (Details) $ in Millions	Mar. 31, 2019 USD ($)
Leases [Abstract]
2019 (Excluding the three months ended March 31, 2019)	$ 24
2020	40
2021	42
2022	39
2023	33
Thereafter	202
Total lease payments	380
Less: Discount	(72)
Total operating lease liabilities	$ 308