Fair Value (Schedule of Fair Value, Assets and Liabilities Measured on Recurring Basis) (Details) - USD ($) $ in Millions	Dec. 31, 2017	Dec. 31, 2016
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale securities	$ 252	$ 299
Trading securities	37	80
Fair value of interest rate swap agreements	1
Total assets	290	379
Contingent Value Right (CVR)	2	1
CVR-related liability	256	252
Fair value of interest rate swap agreements	18	49
Total liabilities	276	302
Fair Value, Inputs, Level 1 [Member] | Fair Value, Measurements, Recurring [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale securities	132	163
Trading securities	37	80
Total assets	169	243
Contingent Value Right (CVR)	2	1
Total liabilities	2	1
Fair Value, Inputs, Level 2 [Member] | Fair Value, Measurements, Recurring [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale securities	120	136
Fair value of interest rate swap agreements	1
Total assets	121	136
Fair value of interest rate swap agreements	18	49
Total liabilities	18	49
Fair Value, Inputs, Level 3 [Member] | Fair Value, Measurements, Recurring [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
CVR-related liability	256	252
Total liabilities	$ 256	$ 252