Financing - Equity Units (Details) - USD ($)	1 Months Ended
	Aug. 31, 2019	Sep. 30, 2019
Financial Instruments Subject to Mandatory Redemption by Settlement Terms [Line Items]
Number of shares indexed (in shares)	34,500,000
Equity units, per unit issuance price (in dollars per share)	$ 50
Proceeds from issuance of mandatory redeemable capital securities	$ 1,682,000,000
Maximum number of shares (in shares)	30,200,000
Junior Subordinated Debt
Financial Instruments Subject to Mandatory Redemption by Settlement Terms [Line Items]
Contract adjustment payments, accretion period	3 years
Series 2019A Remarketable Junior Subordinated Notes | Junior Subordinated Debt
Financial Instruments Subject to Mandatory Redemption by Settlement Terms [Line Items]
Debt face amount	$ 1,725,000,000
Equity units, percentage interest in attached debt instrument	0.0025%
Series 2019B Remarketable Junior Subordinated Notes | Junior Subordinated Debt
Financial Instruments Subject to Mandatory Redemption by Settlement Terms [Line Items]
Equity units, percentage interest in attached debt instrument	0.0025%
Series 2019A And Series 2019B Remarketable Junior Subordinated Notes | Junior Subordinated Debt
Financial Instruments Subject to Mandatory Redemption by Settlement Terms [Line Items]
Distribution rate, percentage	6.75%
Interest rate	2.70%
Contract adjustment rate, percentage	4.05%
Purchase contract adjustment liability		$ 198,000,000
Purchase contract adjustment liability, current		$ 63,000,000
Anti-Dilution Scenario One
Financial Instruments Subject to Mandatory Redemption by Settlement Terms [Line Items]
Equity units, coversion ratio (in shares)	0.7284
Anti-Dilution Scenario One | Minimum
Financial Instruments Subject to Mandatory Redemption by Settlement Terms [Line Items]
Equity units, stock price upper threshold (in dollars per share)	$ 68.64
Anti-Dilution Scenario Two
Financial Instruments Subject to Mandatory Redemption by Settlement Terms [Line Items]
Equity units, per unit issuance price (in dollars per share)	50
Anti-Dilution Scenario Two | Minimum
Financial Instruments Subject to Mandatory Redemption by Settlement Terms [Line Items]
Equity units, stock price lower threshold (in dollars per share)	57.20
Anti-Dilution Scenario Two | Maximum
Financial Instruments Subject to Mandatory Redemption by Settlement Terms [Line Items]
Equity units, stock price upper threshold (in dollars per share)	$ 68.64
Anti-Dilution Scenario Three
Financial Instruments Subject to Mandatory Redemption by Settlement Terms [Line Items]
Equity units, coversion ratio (in shares)	0.8741
Anti-Dilution Scenario Three | Maximum
Financial Instruments Subject to Mandatory Redemption by Settlement Terms [Line Items]
Equity units, stock price lower threshold (in dollars per share)	$ 57.20