Debt - Short-term and Long-term Debt by Issuance (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017	Apr. 30, 2017
Schedule of Debt [Line Items]
Revolving Credit Facilities	$ 0	$ 0
Total Notes and Debentures	4,982	4,795
Unamortized discount and debt issuance cost [2]	134	117
Total Debt	4,848	4,678
Less: Current maturities	500	413
Long-Term Debt	$ 4,348	4,265
Derivative, Fixed Interest Rate	4.39%			4.39%
Interest Expense	$ 259	298	$ 316
6.0% Notes, due 2019
Schedule of Debt [Line Items]
Senior Notes and Debentures	0	413
5.5% Notes, due 2020
Schedule of Debt [Line Items]
Senior Notes and Debentures	500	500
5.125% Notes, due 2022
Schedule of Debt [Line Items]
Senior Notes and Debentures	0	800
2.8% Notes, due 2029
Schedule of Debt [Line Items]
Senior Notes and Debentures	600	0
5.95% Notes, due 2036
Schedule of Debt [Line Items]
Senior Notes and Debentures	300	300
6.625% Notes, due 2040
Schedule of Debt [Line Items]
Senior Notes and Debentures	295	295
6.1% Notes, due 2041
Schedule of Debt [Line Items]
Senior Notes and Debentures	409	409
Unamortized discount and debt issuance cost [2]	76	$ 78
Debt Instrument, Interest Rate, Effective Percentage		7.90%
6.625% Notes, due 2042
Schedule of Debt [Line Items]
Senior Notes and Debentures	178	$ 178
4.4% Notes, due 2048
Schedule of Debt [Line Items]
Senior Notes and Debentures	500	500
3.6% Notes, due 2049
Schedule of Debt [Line Items]
Senior Notes and Debentures	800	0
4.3% Notes, due 2043
Schedule of Debt [Line Items]
Senior Notes and Debentures	300	300
7.875% Notes, due 2042
Schedule of Debt [Line Items]
Junior Subordinated Debentures	600	600
3 Month LIBOR 2.125% Notes, due 2067 [1]
Schedule of Debt [Line Items]
Junior Subordinated Debentures	$ 500	$ 500