Notes Payable - Schedule of Long Term Debt (Details) - USD ($)	Sep. 30, 2020	Dec. 31, 2019	Aug. 13, 2018	Aug. 28, 2012
Debt Instrument [Line Items]
Debt	$ 2,664,000,000	$ 838,000,000
4.50% Notes, net of discount
Debt Instrument [Line Items]
Debt instrument, interest rate, stated percentage			4.50%
3.40% Notes, net of discount
Debt Instrument [Line Items]
Debt instrument, interest rate, stated percentage	3.40%
Debt	$ 643,000,000	0
2.45% Notes, net of discount
Debt Instrument [Line Items]
Debt instrument, interest rate, stated percentage	2.45%
Debt	$ 592,000,000	0
5.50% F& G Notes
Debt Instrument [Line Items]
Debt instrument, interest rate, stated percentage	5.50%
Debt	$ 589,000,000	0
Unsecured notes | 4.50% Notes, net of discount
Debt Instrument [Line Items]
Debt instrument, interest rate, stated percentage	4.50%
Debt	$ 443,000,000	443,000,000
Unsecured notes | 5.50% Notes, net of discount
Debt Instrument [Line Items]
Debt instrument, interest rate, stated percentage	5.50%			5.50%
Debt	$ 399,000,000	398,000,000
Line of Credit | Revolving Credit Facility | Revolving Credit Facility
Debt Instrument [Line Items]
Debt	$ 2,000,000	$ 3,000,000