Debt (Narrative) (Details) - USD ($)	3 Months Ended
	Mar. 31, 2020	May 18, 2020	May 04, 2020	Apr. 30, 2020	Dec. 31, 2019
Line of Credit Facility [Line Items]
Face value of debt	$ 19,040,000,000.00				$ 19,230,000,000
Senior Notes [Member]
Line of Credit Facility [Line Items]
Long-term debt	$ 800,000,000
4.75% Senior Notes due 2025 [Member] | Subsequent Event [Member]
Line of Credit Facility [Line Items]
Face value of debt				$ 1,250,000,000
Stated interest rate				4.75%
4.95% Senior Notes due 2031 [Member] | Subsequent Event [Member]
Line of Credit Facility [Line Items]
Face value of debt				$ 1,250,000,000
Stated interest rate				4.95%
4.30% Senior Notes due 2021 [Member]
Line of Credit Facility [Line Items]
Stated interest rate	4.30%
4.30% Senior Notes due 2021 [Member] | Subsequent Event [Member]
Line of Credit Facility [Line Items]
Debt redeemed			$ 300,000,000
4.50% Senior Notes due 2021 [Member]
Line of Credit Facility [Line Items]
Stated interest rate	4.50%
4.50% Senior Notes due 2021 [Member] | Forecast [Member]
Line of Credit Facility [Line Items]
Debt redeemed		$ 500,000,000
5.875% Junior Subordinated Debentures due 2057 [Member]
Line of Credit Facility [Line Items]
Stated interest rate	5.875%
5.875% Junior Subordinated Debentures due 2057 [Member] | London Interbank Offered Rate (LIBOR) [Member]
Line of Credit Facility [Line Items]
Basis spread on variable rate	3.895%
6.25% Junior Subordinated Debentures due 2057 [Member]
Line of Credit Facility [Line Items]
Stated interest rate	6.25%
6.25% Junior Subordinated Debentures due 2057 [Member] | London Interbank Offered Rate (LIBOR) [Member]
Line of Credit Facility [Line Items]
Basis spread on variable rate	3.899%