Commitments and Contingencies - Litigation and Regulatory Matters (Details)	1 Months Ended	3 Months Ended
	Oct. 31, 2016 lawsuit	Mar. 31, 2018 USD ($)	Mar. 31, 2017 USD ($)
Loss Contingencies [Line Items]
Litigation settlement expense		$ 116,000,000	$ 274,000,000
Minimum
Loss Contingencies [Line Items]
Estimated range of possible loss		0
Maximum
Loss Contingencies [Line Items]
Estimated range of possible loss		$ 1,200,000,000
Waldrup and Williams, et al
Loss Contingencies [Line Items]
Number of lawsuits \| lawsuit	2