Valuation and Qualifying Accounts (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
For Doubtful Receivables [Member]
Movement in Valuation Allowances and Reserves [Roll Forward]
Balance at beginning of year	$ 94	$ 110	$ 148
Valuation Allowances and Reserves, Additions for Charges to Cost and Expense	31	24	53
Valuation Allowances and Reserves, Charged to Other Accounts	0	2	8
Deductions from reserves	15	42	99
Balance at end of year	110	94	110
Other Investments and Noncurrent Receivables [Member]
Movement in Valuation Allowances and Reserves [Roll Forward]
Balance at beginning of year	494	477	454
Valuation Allowances and Reserves, Additions for Charges to Cost and Expense	153	108	62
Valuation Allowances and Reserves, Charged to Other Accounts	0	0	0
Deductions from reserves	289	91	39
Balance at end of year	358	494	477
Valuation Allowance of Deferred Tax Assets [Member]
Movement in Valuation Allowances and Reserves [Roll Forward]
Balance at beginning of year	1,000	1,106	1,112
Valuation Allowances and Reserves, Additions for Charges to Cost and Expense	155	67	126
Valuation Allowances and Reserves, Charged to Other Accounts	0	0	0
Deductions from reserves	94	173	132
Balance at end of year	$ 1,061	$ 1,000	$ 1,106