Effective interest rate for the funds borrowed under the debt agreement considering interest compounding and original issue discount or premium.

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
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Amount, after unamortized (discount) premium and debt issuance costs, of long-term debt. Includes, but not limited to, notes payable, bonds payable, debentures, mortgage loans and commercial paper. Excludes capital lease obligations.

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The amount for notes payable (written promise to pay), due to related parties.

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Condensed Financial Information (Parent Company) (Long-term Debt Outstanding) (Details) - Parent Company - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Sep. 30, 2016
Long-term Debt [Abstract]
Senior Notes	$ 14,599	$ 15,505
Notes Payable, Related Parties	2,000	3,100
Long-term Debt	$ 16,599	18,605
Senior Notes, Unaffiliated [Member]
Long-term Debt [Abstract]
Weighted Average Interest Rate	4.84%
Debt Instrument, Maturity Date Range, Start	Aug. 15, 2018
Debt Instrument, Maturity Date Range, End	May 13, 2046
Senior Notes	$ 14,599	15,505
Senior Notes, Affiliated [Member]
Long-term Debt [Abstract]
Debt Instrument, Interest Rate, Effective Percentage			3.03%
Weighted Average Interest Rate	4.58%
Debt Instrument, Maturity Date Range, Start	Jun. 30, 2019
Debt Instrument, Maturity Date Range, End	Dec. 16, 2021
Senior Notes			$ 250
Notes Payable, Related Parties	$ 2,000	$ 3,100
Minimum \| Senior Notes, Unaffiliated [Member]
Long-term Debt [Abstract]
Debt Instrument, Interest Rate, Effective Percentage	3.00%
Minimum \| Senior Notes, Affiliated [Member]
Long-term Debt [Abstract]
Debt Instrument, Interest Rate, Effective Percentage	3.03%
Maximum \| Senior Notes, Unaffiliated [Member]
Long-term Debt [Abstract]
Debt Instrument, Interest Rate, Effective Percentage	7.72%
Maximum \| Senior Notes, Affiliated [Member]
Long-term Debt [Abstract]
Debt Instrument, Interest Rate, Effective Percentage	5.86%