Debt Level 4 (Details) - USD ($)	12 Months Ended			240 Months Ended	600 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013	Apr. 15, 2042	Jun. 15, 2068	Nov. 02, 2015	May. 27, 2015	Mar. 30, 2015	Jun. 30, 2012
Short-term Debt [Abstract]
Long-term Line of Credit	$ 0	$ 0
Notes Payable	5,359,000,000	6,109,000,000
Long-term Debt, Excluding Current Maturities	5,084,000,000	5,653,000,000
Current maturity adjustment to long-term debt	(275,000,000)	(456,000,000)
Debt, Long-term and Short-term, Combined Amount	5,359,000,000	6,109,000,000
Debt Instrument, Interest Rate, Stated Percentage [Abstract]
Interest Expense	357,000,000	376,000,000	$ 397,000,000
Financial Instruments Owned and Pledged as Collateral, Amount Eligible to be Repledged by Counterparty	1,200,000,000
Maximum Aggregate Principal Amount of Junior Subordinated Notes	500,000,000
Loss on extinguishment of debt	(21,000,000)	0	$ (213,000,000)
Long-term Federal Home Loan Bank Advances	0
Line of Credit Facility [Abstract]
Commercial Paper	1,000,000,000
Maturities of Long-term Debt [Abstract]
Long-term Debt, Maturities, Repayments of Principal in Next Twelve Months	275,000,000
Long-term Debt, Maturities, Repayments of Principal in Year Two	416,000,000
Long-term Debt, Maturities, Repayments of Principal in Year Three	320,000,000
Long-term Debt, Maturities, Repayments of Principal in Year Four	413,000,000
Long-term Debt, Maturities, Repayments of Principal in Year Five	500,000,000
Long-term Debt, Maturities, Repayments of Principal after Year Five	3,525,000,000
Commercial Paper, Outstanding	0
Debt Instrument, Repurchased Face Amount							$ 0
Debt Instrument, Repurchase Amount						$ 0	$ 0	$ 0
Five Year Revolving Credit Facility [Member]
Line of Credit Facility [Abstract]
Line of Credit Facility, Maximum Borrowing Capacity	1,000,000,000
Borrowings [Member]
Line of Credit Facility [Abstract]
Line of Credit Facility, Maximum Amount Outstanding During Period	0
Senior Note Five Point Five Percent Due in Two Thousand Sixteen [Member]
Short-term Debt [Abstract]
Senior Notes	275,000,000
Senior Note Seven Point Three Percent Due in Two Thousand Fifteen [Member]
Short-term Debt [Abstract]
Senior Notes	$ 0
Revolving Credit Facility [Member] | Four Year Revolving Credit Facility [Member]
Line of Credit Facility [Abstract]
Line of Credit, Term of Credit Facility	4 years
Revolving Credit Facility [Member] | Five Year Revolving Credit Facility [Member]
Line of Credit Facility [Abstract]
Line of Credit, Term of Credit Facility	5 years
Senior Note Four Point Zero Percent Due in Two Thousand Fifteen [Member]
Short-term Debt [Abstract]
Senior Notes	$ 0
Senior Note Four Point Zero Percent Due in Two Thousand Fifteen [Member]
Short-term Debt [Abstract]
Senior Notes		289,000,000
Debt Instrument, Interest Rate, Stated Percentage [Abstract]
Debt Instrument, Interest Rate, Stated Percentage	4.00%
Senior Note Seven Point Three Percent Due in Two Thousand Fifteen [Member]
Short-term Debt [Abstract]
Senior Notes		167,000,000
Debt Instrument, Interest Rate, Stated Percentage [Abstract]
Debt Instrument, Interest Rate, Stated Percentage	7.30%
Senior Note Five Point Five Percent Due in Two Thousand Sixteen [Member]
Short-term Debt [Abstract]
Senior Notes		275,000,000
Debt Instrument, Interest Rate, Stated Percentage [Abstract]
Debt Instrument, Interest Rate, Stated Percentage	5.50%
Senior Note 5.375% Due 2017 [Member]
Short-term Debt [Abstract]
Senior Notes	$ 416,000,000	415,000,000
Debt Instrument, Interest Rate, Stated Percentage [Abstract]
Debt Instrument, Interest Rate, Stated Percentage	5.375%
Senior Note 4.0% Due 2017 [Member]
Short-term Debt [Abstract]
Senior Notes	$ 0	295,000,000
Debt Instrument, Interest Rate, Stated Percentage [Abstract]
Debt Instrument, Interest Rate, Stated Percentage	4.00%
Senior Note 6.3% Due 2018 [Member]
Short-term Debt [Abstract]
Senior Notes	$ 320,000,000	320,000,000
Debt Instrument, Interest Rate, Stated Percentage [Abstract]
Debt Instrument, Interest Rate, Stated Percentage	6.30%
Senior Note 6.0% Due 2019 [Member]
Short-term Debt [Abstract]
Senior Notes	$ 413,000,000	413,000,000
Debt Instrument, Interest Rate, Stated Percentage [Abstract]
Debt Instrument, Interest Rate, Stated Percentage	6.00%
Senior Note 5.5% Due 2020 [Member]
Short-term Debt [Abstract]
Senior Notes	$ 499,000,000	499,000,000
Debt Instrument, Interest Rate, Stated Percentage [Abstract]
Debt Instrument, Interest Rate, Stated Percentage	5.50%
Senior Note 5.125% Due 2022 [Member]
Short-term Debt [Abstract]
Senior Notes	$ 797,000,000	797,000,000
Debt Instrument, Interest Rate, Stated Percentage [Abstract]
Debt Instrument, Interest Rate, Stated Percentage	5.125%
Senior Note 7.65% Due 2027 [Member]
Short-term Debt [Abstract]
Senior Notes	$ 80,000,000	80,000,000
Debt Instrument, Interest Rate, Stated Percentage [Abstract]
Debt Instrument, Interest Rate, Stated Percentage	7.65%
Senior Note 7.375% Due 2031 [Member]
Short-term Debt [Abstract]
Senior Notes	$ 63,000,000	63,000,000
Debt Instrument, Interest Rate, Stated Percentage [Abstract]
Debt Instrument, Interest Rate, Stated Percentage	7.375%
Senior Note 5.95% Due 2036 [Member]
Short-term Debt [Abstract]
Senior Notes	$ 299,000,000	299,000,000
Debt Instrument, Interest Rate, Stated Percentage [Abstract]
Debt Instrument, Interest Rate, Stated Percentage	5.95%
Senior Note 6.625% Due 2040 [Member]
Short-term Debt [Abstract]
Senior Notes	$ 295,000,000	295,000,000
Debt Instrument, Interest Rate, Stated Percentage [Abstract]
Debt Instrument, Interest Rate, Stated Percentage	6.625%
Senior Note 6.1% Due 2041 [Member]
Short-term Debt [Abstract]
Senior Notes	$ 326,000,000	326,000,000
Debt Instrument, Interest Rate, Stated Percentage [Abstract]
Debt Instrument, Interest Rate, Stated Percentage	6.10%
Debt Instrument, Interest Rate, Effective Percentage	7.90%
Senior Note 6.625% Due 2042 [Member]
Short-term Debt [Abstract]
Senior Notes	$ 178,000,000	178,000,000
Debt Instrument, Interest Rate, Stated Percentage [Abstract]
Debt Instrument, Interest Rate, Stated Percentage	6.625%
Senior Note 4.3% Due in 2043 [Member]
Short-term Debt [Abstract]
Senior Notes	$ 298,000,000	298,000,000
Debt Instrument, Interest Rate, Stated Percentage [Abstract]
Debt Instrument, Interest Rate, Stated Percentage	4.30%
7.875% Notes, due 2042 [Member]
Short-term Debt [Abstract]
Junior Subordinated Notes	$ 600,000,000	600,000,000
Debt Instrument, Interest Rate, Stated Percentage [Abstract]
Debt Instrument, Interest Rate, Stated Percentage	7.875%
8.125% Notes, due 2068 [Member]
Short-term Debt [Abstract]
Junior Subordinated Notes	$ 500,000,000	$ 500,000,000
Debt Instrument, Interest Rate, Stated Percentage [Abstract]
Debt Instrument, Interest Rate, Stated Percentage	8.125%
Fair Value, Estimate Not Practicable, Maturity Date [Member]
Short-term Debt [Abstract]
Senior Notes									$ 0.061
Scenario, Forecast [Member] | 7.875% Notes, due 2042 [Member]
Debt Instrument, Interest Rate, Stated Percentage [Abstract]
Debt Instrument, Interest Rate Terms				3 Month LIBOR + 5.596%
Scenario, Forecast [Member] | 8.125% Notes, due 2068 [Member]
Debt Instrument, Interest Rate, Stated Percentage [Abstract]
Debt Instrument, Interest Rate Terms					3 Month LIBOR + 4.6025%