Debt (Narrative) (Details) - USD ($)	3 Months Ended		6 Months Ended
	Jun. 30, 2020	Jun. 30, 2019	Jun. 30, 2020	Jun. 30, 2019	Jul. 10, 2020	Dec. 31, 2019
Line of Credit Facility [Line Items]
Face value of debt	$ 20,690,000,000		$ 20,690,000,000			$ 19,230,000,000
Loss on extinguishment of debt	$ 103,000,000	$ 0	$ 103,000,000	$ 0
3.875% Senior Notes due 2021 [Member]
Line of Credit Facility [Line Items]
Stated interest rate	3.875%		3.875%
5.875% Junior Subordinated Debentures due 2057 [Member]
Line of Credit Facility [Line Items]
Stated interest rate	5.875%		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%
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%
Senior Notes [Member]
Line of Credit Facility [Line Items]
Face value of debt	$ 4,500,000,000		$ 4,500,000,000
Senior Notes [Member] | Minimum [Member]
Line of Credit Facility [Line Items]
Stated interest rate	4.20%		4.20%
Senior Notes [Member] | Maximum [Member]
Line of Credit Facility [Line Items]
Stated interest rate	4.95%		4.95%
Senior Notes [Member] | 3.875% Senior Notes due 2021 [Member] | Subsequent Event [Member]
Line of Credit Facility [Line Items]
Stated interest rate					3.875%
Debt redeemed					$ 340,000,000
Senior Notes and Junior Subordinated Debentures [Member]
Line of Credit Facility [Line Items]
Debt redeemed	$ 2,430,000,000		$ 2,430,000,000
Payments for debt redemption			2,520,000,000
Unamortized debt issuance costs and fees	$ 15,000,000		$ 15,000,000